LOW-TECH MAGAZINEtag:typepad.com,2003:weblog-13761342019-06-01T20:57:43+02:00Doubts on progress and technology
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TypePadReinventing the Small Wind Turbinetag:typepad.com,2003:post-6a00e0099229e888330240a4af9677200b2019-06-01T20:57:43+02:002019-06-05T00:29:02+02:00Many commercially available small wind turbines with plastic blades and steel towers are infamous for their low reliability, high embodied energy, and limited power output. Building them out of wood can address these issues. Because of their aesthetic appeal, and thanks to the ability to produce them locally, small wooden wind turbines can also improve the public acceptance of wind power. Furthermore, innovation in tower design facilitates the installation of small wind turbines, reducing the need for concrete foundations and heavy machinery. Image: A wind turbine with wooden blades. Source: EAZ Wind. Low Performance Tests have shown that commercially available small wind turbines may not always generate sufficient power over their lifetime to compensate for the energy that was needed...kris de decker
<div xmlns="http://www.w3.org/1999/xhtml"><p><a class="asset-img-link" style="float: right;" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4af994a200b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330240a4af994a200b img-responsive" style="width: 500px; margin: 0px 0px 5px 5px;" alt="Detail-eaz-wind" title="Detail-eaz-wind" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4af994a200b-500wi" /></a></p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4af9924200b-pi"></a>Many commercially available small wind turbines with plastic blades and steel towers are infamous for their low reliability, high embodied energy, and limited power output.</p>
<p>Building them out of wood can address these issues. Because of their aesthetic appeal, and thanks to the ability to produce them locally, small wooden wind turbines can also improve the public acceptance of wind power.</p>
<p>Furthermore, innovation in tower design facilitates the installation of small wind turbines, reducing the need for concrete foundations and heavy machinery.&nbsp;</p>
<p style="text-align: right;"><span style="background-color: #f7dde9;">Image: A wind turbine with wooden blades. Source: EAZ Wind.</span></p>
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<h2 style="text-align: center;"><strong><span style="color: #c00000;">Low Performance</span></strong></h2>
<p>Tests have shown that commercially available small wind turbines <a href="http://theoildrum.com/node/6954">may not always generate sufficient power over their lifetime</a> to compensate for the energy that was needed to produce them. There are three reasons why this is so. First, there are the laws of physics. The energy yield of a wind turbine increases faster than its height and rotor size, meaning that as a wind turbine becomes smaller, <a href="https://www.lowtechmagazine.com/2008/09/urban-windmills.html">its power output decreases over proportionally</a>.</p>
<p>Second, wind turbine blades are commonly made from fiberglass reinforced plastic, which is energy-intensive to produce (<a href="https://www.lowtechmagazine.com/2019/06/large-wooden-wind-turbines.html">and impossible to recycle</a>). This energy needs to be “paid back” during the lifetime of the wind turbine, which can be challenging for machines with small rotor diameters.</p>
<p>Third, the maintenance of small wind turbines depends on the ability of the manufacturer to remain in business and provide its customers with spare parts. Unlike solar panels, wind turbines have a lot of moving parts and are thus more likely to need repairs. However, suppliers of small wind turbines tend to have an even shorter life expectancy than their products. [<span style="color: #c00000;">1</span>]</p>
<h2 style="text-align: center;"><span style="color: #c00000;"><strong>Hand Carved Wood Blades</strong></span></h2>
<p>The laws of physics can’t be changed, but on their own they don’t make small wind turbines uneconomical and unsustainable. It’s the other two factors that are decisive, and these can be addressed. In fact, they have been addressed for more than two decades by <a href="http://scoraigwind.co.uk">Scottish engineer Hugh Piggott</a>, who builds small 1-2 kW wind turbines with 2-4 meter rotor diameters using solid wooden blades. [<span style="color: #c00000;">2</span>]</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a48b1f1f200d-pi"><img class="asset asset-image at-xid-6a00e0099229e888330240a48b1f1f200d img-responsive" style="width: 700px; display: block; margin-left: auto; margin-right: auto;" alt="Nepali-hand-carved-blades-mishnaevsky-2009" title="Nepali-hand-carved-blades-mishnaevsky-2009" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a48b1f1f200d-700wi" /></a></p>
<p style="text-align: center;"><span style="color: #111111; background-color: #f7dde9;">Hand carved wooden blades. Source: [5]</span></p>
<p>The blades are hand carved locally with basic woodworking skills and tools. In contrast to fiberglass blades, little or no energy is used to produce them. This increases the chance that the wind turbine will produce more energy over its lifetime than was needed to make it.</p>
<p>Defying the usual focus on efficiency, Piggott’s wind turbines sacrifice peak power for more reliable operation. The machines use a furling system which limits the turbine input at winds of 8 m/s (Beaufort 5), while most commercial models keep working up to higher wind speeds. This increases reliability, because the faster the machine spins, the quicker its parts will wear out. [<span style="color: #c00000;">3</span>]</p>
<h2 style="text-align: center;"><span style="color: #c00000;"><strong>Local Manufacturing</strong></span></h2>
<p>A comparison of Piggott’s wind turbines with commercially available models concluded that the increased energy yield generated by the latter at wind speeds above 8 m/s is largely wasted, because most of the extra power is generated when the batteries are already full. The study also revealed that the Scottish design is about 20% cheaper, taking into account both capital and operational costs. [<span style="color: #c00000;">3</span>]</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a461c2ce200c-pi"><img class="asset asset-image at-xid-6a00e0099229e888330240a461c2ce200c img-responsive" style="width: 700px; display: block; margin-left: auto; margin-right: auto;" alt="Installation-wind-turbines-wood-blades-nepal-mishnaevsky-2011" title="Installation-wind-turbines-wood-blades-nepal-mishnaevsky-2011" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a461c2ce200c-700wi" /></a></p>
<p style="text-align: center;"><span style="background-color: #f7dde9;">Wooden wind turbines in Nepal. Source: [<span style="color: #c00000;">5</span>]</span></p>
<p>Piggott’s open source design has spawned thousands of small DIY wind turbines all over the world. It also became the basis for several wind-based rural electrification initiatives in Mongolia, Nepal, Peru and Nicaragua. [<span style="color: #c00000;">4-7</span>] In “developing” countries, the ability to manufacture and maintain the turbines locally is a great advantage over the use of commercial wind turbines or solar panels.</p>
<h2 style="text-align: center;"><strong><span style="color: #c00000;">Commercial Wind Turbines with Wood Blades</span></strong></h2>
<p>The use of solid wood blades, <a href="https://www.notechmagazine.com/2009/12/windmills-and-wind-motors-how-to-build-and-run-them-1910.html">once common</a> for <a href="https://www.notechmagazine.com/2011/05/the-homemade-windmills-of-nebraska-1899.html">smaller windmills and wind turbines</a>, has seen renewed interest lately. [<span style="color: #c00000;">8-9</span>] Most notable is the success story of the Dutch company <a href="https://www.eazwind.com/en/home-3/">EAZ Wind</a>, founded in 2014 by four young windsurfers. The firm, which now has over 40 employees, sells wind turbines with solid wooden blades to farms and energy cooperatives in the region. With a rotor diameter of 12 meter and a power output of 10 kW, the turbines are about five times larger than Piggott’s machines.</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4af9924200b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330240a4af9924200b img-responsive" alt="EAZ-Twaalf-Overzicht" title="EAZ-Twaalf-Overzicht" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4af9924200b-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p style="text-align: center;"><span style="background-color: #f7dde9;">Wind turbine with wooden blades, built by EAZ Wind.&nbsp;</span></p>
<p>The blades are made from solid wood beams that are glued together and then sanded to obtain their shape. They are then covered with an epoxy coating to protect them from humidity, while the sharp side of the blade gets a strip of fiberglass reinforced plastic to make it more durable.</p>
<p>According to the manufacturer, the wind turbines -- installed on 15 m tall towers -- produce roughly 30,000 kWh of electricity per year, which corresponds to the power use of ten Dutch households. A machine sells for 46,000 euro, which makes it cheaper than a solar PV system (4,600 euro per household, or less than half the price of a solar PV system). The financial payback time – in the windy northern Netherlands – is 7 to 10 years.</p>
<h2 style="text-align: center;"><span style="color: #c00000;"><strong>Public Acceptance</strong></span></h2>
<p>Interestingly, EAZ Wind’s choice for wooden blades is not driven by the aim to lower the embodied energy of the wind turbine. Rather, the company’s mission is to make the countryside – especially farms but also small villages – self-sufficient in terms of power production by designing more beautiful and locally produced wind turbines that people don’t complain about. As in many other countries, large wind turbines – and the transmission lines that go with them – raise a lot of opposition from local residents in the Netherlands.</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a48b2081200d-pi"><img class="asset asset-image at-xid-6a00e0099229e888330240a48b2081200d img-responsive" style="width: 700px; display: block; margin-left: auto; margin-right: auto;" alt="EAZ-wind-blades" title="EAZ-wind-blades" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a48b2081200d-700wi" /></a></p>
<p style="text-align: center;"><span style="background-color: #f7dde9;">Installing a wind turbine. Image: EAZ Wind.</span></p>
<p>The approach seems to work. When a farm installs a wind turbine, its neighbours are usually the next customers. EAZ Wind has sold more than 400 wind turbines by now. Public acceptance of wind power seems to be encouraged by two factors. First, wind turbines with wooden blades have a more natural look, increasing their aesthetic appeal.</p>
<p>Second, the machines are produced locally, meaning that the purchase of a wind turbine supports the local economy. The wood for the blades comes from a nearby province and is processed by companies in the region.</p>
<h2 style="text-align: center;"><strong><span style="color: #c00000;">Wooden Towers</span></strong></h2>
<p>The turbines from EAZ Wind have wooden blades, but steel towers. The Swedish company <a href="https://www.innoventum.se">InnoVentum</a>&nbsp;takes a different approach: its wind turbines have a wooden tower, while the blades are made from plastic. The 12 m or 20 m tall towers are of a unique design, composed from small wood modules that can be bolted together on the ground in a few hours.</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4af986c200b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330240a4af986c200b img-responsive" style="width: 692px; display: block; margin-left: auto; margin-right: auto;" alt="Innoventum2" title="Innoventum2" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4af986c200b-700wi" /></a></p>
<p style="text-align: center;"><span style="background-color: #f7dde9;">Innoventum's wooden wind turbine tower.&nbsp;</span></p>
<p>The multi-leg towers require <a href="https://www.innoventum.se/portfolio/dalifant-inst-se/">no -- or much less -- concrete for their foundations</a> and they can be erected without the use of a crane, using a rope and a winch instead. Around fifteen have been installed since 2012. Like EAZ Wind, the company aims to create a new aesthetic level that may help to increase the acceptance of wind turbines.</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4af988b200b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330240a4af988b200b img-responsive" style="width: 700px; display: block; margin-left: auto; margin-right: auto;" alt="Innoventum3" title="Innoventum3" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4af988b200b-700wi" /></a></p>
<p style="text-align: center;"><span style="background-color: #f7dde9;">Innoventum's wooden wind turbine tower.&nbsp;</span></p>
<p>Of course, both approaches could be combined, resulting in small wind turbines with wooden blades, tower and other structural parts. A small wind turbine that’s almost completely built out of wood – minus the gearwork and the generator – further decreases the energy that’s needed to produce it, thus making it more economical and sustainable over its entire lifetime.</p>
<p>In terms of carbon emissions, a small wooden wind turbine can even be considered a carbon sink, because the wood sequesters CO2 that the trees have taken from the atmosphere.&nbsp;</p>
<p style="text-align: center;"><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4afd975200b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330240a4afd975200b img-responsive" style="width: 700px; display: block; margin-left: auto; margin-right: auto;" alt="Wooden-blades-and-tower" title="Wooden-blades-and-tower" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4afd975200b-700wi" /></a></p>
<p style="text-align: center;"><span style="background-color: #f7dde9;">Wind turbine with wooden blades and tower. InnoVentum.</span></p>
<h2 style="text-align: center;"><strong><span style="color: #c00000;">Combining Wind and Solar</span></strong></h2>
<p>The newest products from both EAZ Wind and InnoVentum incorporate solar panels at the basis of the structure. Because the wind turbine and the solar PV system can share the same support structure, electrical system, and energy storage, this approach saves money and resources. The combination of solar and wind also increases the chances of sufficient power output at any time, reducing the need for energy storage – which is the <a href="https://www.lowtechmagazine.com/2015/05/sustainability-off-grid-solar-power.html">most unsustainable part of an off-the-grid power installation</a>.</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4af9895200b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330240a4af9895200b img-responsive" style="width: 700px; display: block; margin-left: auto; margin-right: auto;" alt="IMG_4468_1_for_collage-e1470916572514" title="IMG_4468_1_for_collage-e1470916572514" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a4af9895200b-700wi" /></a></p>
<p style="text-align: center;"><span style="background-color: #f7dde9;">Solar panels and wind turbine use the same supporting structure. Image: InnoVentum.</span></p>
<p>In the hybrid solar-wind model from EAZ Wind, the capacity of the wind turbine is double the capacity of the solar PV panels, reflecting the local climate (windy but not very sunny). The addition of solar panels increases the power yield to 45,000 kWh per year, which corresponds to the power demand of 14 Dutch households. However, the use of solar panels <a href="https://www.lowtechmagazine.com/2015/04/how-sustainable-is-pv-solar-power.html">increases the embodied energy of the system considerably</a>, so that it may no longer be a carbon sink.</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a48b1fda200d-pi"><img class="asset asset-image at-xid-6a00e0099229e888330240a48b1fda200d img-responsive" style="width: 700px; display: block; margin-left: auto; margin-right: auto;" alt="INNOVENTUM1" title="INNOVENTUM1" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a48b1fda200d-700wi" /></a></p>
<p style="text-align: center;"><span style="background-color: #f7dde9;">Solar panels and wind turbine use the same supporting structure. Image: InnoVentum.</span></p>
<h2 style="text-align: center;"><span style="color: #c00000;"><strong>Decentralised Power Production</strong></span></h2>
<p>Small wooden wind turbines offer additional benefits that are inherent to all decentralised power sources. The fact that they're paid for by the same people that enjoy their benefits, increases their public acceptance. They also eliminate the need for transmission lines, and the more power is produced and used locally, the less challenging it becomes to integrate unpredictable wind power into the central grid. Last but not least, the connection between energy use and demand <a href="https://www.lowtechmagazine.com/2018/12/keeping-some-of-the-lights-on-redefining-energy-security.html">encourages lower energy ways of life</a>.&nbsp;</p>
<p><a href="https://www.lowtechmagazine.com/2019/06/wooden-wind-turbines.html">Part 2: Could we also build large wind turbines out of wood again?</a></p>
<p>Kris De Decker</p>
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<h2><strong>References:</strong></h2>
<p>[1] Kostakis, Vasilis, et al. "<a href="https://www.minasliarokapis.com/CleanerProduction2016_Kostakis_DigitalCommonsLocalManufacturing.pdf">The convergence of digital commons with local manufacturing from a degrowth perspective: two illustrative cases</a>." Journal of Cleaner Production 197 (2018): 1684-1693.</p>
<p>[2] <a href="https://www.scoraigwind.com/pirate%20oldies/Hugh%20Piggott%20Axial-flow%20PMG%20wind%20turbine%20May%202003.pdf">How to build a wind turbine</a>. High Piggott, 2003.</p>
<p>[3] Sumanik-Leary, Jon, et al. "<a href="http://windempowerment.org/wp-content/uploads/2014/11/PhD_Seminar_2013_FullPaper_Sumanik-Leary-FINAL.pdf">Locally manufactured small wind turbines: how do they compare to commercial machines</a>." Proceedings of 9 th PhD Seminar on Wind Energy in Europe. 2013.</p>
<p>[4] Mishnaevsky, Leon, et al. "<a href="https://www.mdpi.com/1996-1944/10/11/1285">Materials for wind turbine blades: an overview</a>." Materials 10.11 (2017): 1285.</p>
<p>[5] Mishnaevsky Jr, Leon, et al. "<a href="https://www.researchgate.net/profile/Hai_Qing2/publication/242770543_Strength_and_Reliability_of_Wood_for_the_Components_of_Low-cost_Wind_Turbines_Computational_and_Experimental_Analysis_and_Applications/links/590142fa0f7e9bcf65468690/Strength-and-Reliability-of-Wood-for-the-Components-of-Low-cost-Wind-Turbines-Computational-and-Experimental-Analysis-and-Applications.pdf">Strength and reliability of wood for the components of low-cost wind turbines: computational and experimental analysis and applications</a>." Wind Engineering 33.2 (2009): 183-196.</p>
<p>[6] Mishnaevsky Jr, Leon, et al. "<a href="https://www.sciencedirect.com/science/article/pii/S0960148111000565">Small wind turbines with timber blades for developing countries: Materials choice, development, installation and experiences</a>." Renewable Energy 36.8 (2011): 2128-2138.</p>
<p>[7] Sinha, Rakesh, et al. "<a href="https://journals.sagepub.com/doi/abs/10.1260/0309-524X.34.3.263">Selection of Nepalese timber for small wind turbine blade construction</a>." Wind Engineering 34.3 (2010): 263-276.&nbsp;</p>
<p>[8]&nbsp;Clausen, P. D., F. Reynal, and D. H. Wood. "<a href="https://www.sciencedirect.com/science/article/pii/B9780857094261500131">Design, manufacture and testing of small wind turbine blades</a>." Advances in wind turbine blade design and materials. Woodhead Publishing, 2013. 413-431.</p>
<p>[9] Pourrajabian, Abolfazl, et al. "<a href="https://www.sciencedirect.com/science/article/pii/S136403211830710X">Choosing an appropriate timber for a small wind turbine blade: A comparative study</a>." Renewable and Sustainable Energy Reviews 100 (2019): 1-8.</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a461c36f200c-pi"><img class="asset asset-image at-xid-6a00e0099229e888330240a461c36f200c img-responsive" style="width: 700px; display: block; margin-left: auto; margin-right: auto;" alt="21238937803_0fa124fa17_k" title="21238937803_0fa124fa17_k" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a461c36f200c-700wi" /></a></p>
<p style="text-align: center;"><span style="background-color: #f7dde9;">Image: InnoVentum.</span></p>
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Heat your House with a Mechanical Windmilltag:typepad.com,2003:post-6a00e0099229e88833022ad3c52b54200d2019-02-27T11:04:46+01:002019-03-31T15:05:08+02:00Given the right conditions, a mechanical windmill with an oversized brake system is a cheap, effective, and sustainable heating system.kris de decker
<div xmlns="http://www.w3.org/1999/xhtml"><p><a class="asset-img-link" style="float: right;" href="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3c52bd2200d-pi"><img class="asset asset-image at-xid-6a00e0099229e88833022ad3c52bd2200d img-responsive" style="width: 500px; margin: 0px 0px 5px 5px;" alt="Heat generating windmill illustration rona binay" title="Heat generating windmill illustration rona binay" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3c52bd2200d-500wi" /></a></p>
<p>Renewable energy production is almost entirely aimed at the generation of electricity. However, we use more energy in the form of heat, which solar panels and wind turbines can produce only indirectly and relatively inefficiently.&nbsp;</p>
<p>A solar thermal collector skips the conversion to electricity and supplies renewable thermal energy in a direct and more efficient way.</p>
<p>Much less known is that a mechanical windmill can do the same in a windy climate -- by oversizing its brake system, a windmill can generate lots of direct heat through friction. A mechanical&nbsp; windmill can also be coupled to a mechanical heat pump, which can be cheaper than using a gas boiler or an electric heat pump driven by a wind turbine.</p>
<p style="text-align: right;"><span style="background-color: #ecdae5; color: #111111;">Illustration: <span style="text-decoration: underline;"><a href="https://ronabinay.com" style="background-color: #ecdae5; color: #111111; text-decoration: underline;">Rona Binay</a></span> for Low-tech Magazine.</span></p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">Given the right conditions, a mechanical windmill with an oversized brake system is a cheap, effective, and sustainable heating&nbsp;system.</span></p>
</blockquote>
<h2 style="text-align: center;"><span style="color: #c00000;">Heat versus Electricity</span></h2>
<p>On a global scale, thermal energy demand corresponds to one third of the primary energy supply, while electricity demand is only one-fifth. [<span style="color: #c00000;">1</span>] In temperate or cold climates, the share of thermal energy is even higher. For example in the UK, heat counts for almost half of total energy use. [<span style="color: #c00000;">2</span>] If we only look at households, thermal energy for space and water heating in temperate and cold climates can be 60-80% of total domestic energy demand. [<span style="color: #c00000;">3</span>]</p>
<p>In spite of this, renewable energy sources play a negligible role in heat production. The main exception is the traditional use of biomass for cooking and heating – but in the “developed” world even biomass is often used to produce electricity instead of heat. The use of direct solar heat and geothermal heat provide less than 1% and 0.2% of global heat demand, respectively [<span style="color: #c00000;">4</span>] [<span style="color: #c00000;">5</span>]. While renewable energy sources account for more than 20% of global electricity demand (mostly hydroelectric), they only account for 10% of global heat demand (mostly biomass). [<span style="color: #c00000;">5</span>] [<span style="color: #c00000;">6</span>]</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Direct versus Indirect Heat Production</span></h2>
<p>Electricity produced by renewable energy sources can be – and is being – converted to heat in an indirect way. For example, a wind turbine converts its rotational energy into electricity by the use of its electrical generator, and this electricity can then be converted into heat using an electric heater, an electric boiler, or an electric heat pump. The result is heat generated by wind energy.</p>
<p>In particular, the electric heat pump is promoted by many governments and organisations as a sustainable solution for renewable heat generation. However, solar and wind energy can also be used in a direct way, without converting them to electricity first – and of course the same applies to biomass. Direct heat production is cheaper, can be more energy efficient, and is more sustainable than indirect heat production.</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3c530c2200d-pi"><img class="asset asset-image at-xid-6a00e0099229e88833022ad3c530c2200d img-responsive" alt="heat generating windmills" title="heat generating windmills" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3c530c2200d-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p style="text-align: center;"><span style="background-color: #ecdae5;">Prototypes of heat generating windmills, built by Esra L. Sorensen in 1974. Photo by Claus Nybroe. Source: [13]</span></p>
<p>The direct alternative for solar photovoltaic power is solar thermal power, a technology that appeared in the nineteenth century following cheaper production technologies for glass and mirrors. Solar thermal energy can be used for water heating, space heating or industrial processes, and this is <a href="https://www.lowtechmagazine.com/2011/07/solar-powered-factories.html">2-3 times as energy efficient compared to following the indirect path involving electricity conversion</a>.</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">Almost nobody knows that a windmill can produce heat directly.</span></p>
</blockquote>
<p>The direct alternative for wind power that everybody knows is the old-fashioned windmill, which is at least 2.000 years old. It transferred the rotational energy from its wind rotor directly to the axis of a machine, for example for sawing wood or grinding grain. This <a href="https://www.lowtechmagazine.com/2009/10/history-of-industrial-windmills.html">old-fashioned approach remains relevant</a>, also in combination with new technology, because it would be more energy efficient compared to first converting the energy to electricity, and then back to rotational energy.</p>
<p>However, an old-fashioned windmill can not only provide mechanical energy, but also thermal energy. The problem is that almost nobody knows this. Even the International Energy Agency doesn't mention direct conversion of wind into heat when it presents all possible options for renewable heat production. [<span style="color: #c00000;">1</span>]</p>
<h2 style="text-align: center;"><span style="color: #c00000;">The Water Brake Windmill</span></h2>
<p>One type of heat generating windmill converts rotational energy directly into heat by generating friction in water, using a so-called “water brake” or “Joule Machine”. A heat generator based on this principle is basically a wind-powered mixer or impeller installed into an insulated tank filled with water. Due to friction among molecules of the water, mechanical energy is converted into heat energy. The heated water can be pumped into a building for heating or washing, and the same concept could be applied to industrial processes in a factory that require relatively low temperatures. [<span style="color: #c00000;">7</span>] [<span style="color: #c00000;">8</span>] [<span style="color: #c00000;">9</span>]</p>
<p style="text-align: center;"><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad39f1e05200c-pi"><img class="asset asset-image at-xid-6a00e0099229e88833022ad39f1e05200c img-responsive" alt="Drawing of heat generating windmill" title="Drawing of heat generating windmill" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad39f1e05200c-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a><span style="background-color: #ecdae5;">Drawing of a heating system based on a water brake windmill. Source: [8]</span></p>
<p>The Joule Machine was originally conceived as a measuring apparatus. James Joule built it in the 1840s for his famous measurement of the mechanical equivalent of heat: one calorie equals the amount of energy required to raise the temperature of 1 cubic centimeter of water by 1 degree Celsius. [<span style="color: #c00000;">10</span>]</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">A heat generator based on this principle is basically a wind-powered mixer or impeller installed into an insulated tank filled with water</span></p>
</blockquote>
<p>The most fascinating thing about water brake windmills is that, hypothetically, they could have been built hundreds or even thousands of years ago. They require simple materials: wood and/or metal. But although we cannot exclude their use in pre-industrial times, the first reference to heat producing windmills dates from the 1970s, when the Danes started building them in the wake of the first oil crisis.</p>
<p style="text-align: center;"><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3e4dc65200b-pi"><img class="asset asset-image at-xid-6a00e0099229e88833022ad3e4dc65200b img-responsive" alt="heat generator windmill" title="heat generator windmill" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3e4dc65200b-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a><span style="background-color: #ecdae5;">Drawing of the heat generator of a heat generating windmill. Source: [8]</span></p>
<p style="text-align: left;">At the time, Denmark was almost entirely dependent on imported oil for heating, which left many households in the cold when the oil supply was disturbed. Because the Danes already had a strong DIY-culture for small wind turbines generating electricity on farms, they started building windmills to heat their houses. Some chose the indirect path, converting wind generated electricity into heat using electric heating appliances. Others, however, developed mechanical windmills that produced heat directly.</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Cheaper to Build</span></h2>
<p>The direct approach to heat production is considerably cheaper and more sustainable than converting wind or solar generated electricity into heat by using electric heating devices. There’s two reasons for this.</p>
<p>First, and most importantly, mechanical windmills are less complex, which makes them more affordable and less resource-intensive to build, and which increases their lifetime. In a water brake windmill, electric generator, power converters, transformer and gearbox can be excluded, and because of the weight savings, the windmill needs to be less sturdy built. The Joule Machine has lower weight, smaller size, and lower costs than an electrical generator. [<span style="color: #c00000;">11</span>] Also important is that the cost of thermal storage is 60-70% lower compared to batteries or the use of backup thermal power plants. [<span style="color: #c00000;">2</span>]</p>
<p><a class="asset-img-link" style="display: inline;" href="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3c536a7200d-pi"><img class="asset asset-image at-xid-6a00e0099229e88833022ad3c536a7200d img-responsive" alt="Heat-generating-windmill-water-brake" title="Heat-generating-windmill-water-brake" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3c536a7200d-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p style="text-align: center;"><span style="background-color: #ecdae5;">A water brake windmill built at the Institute for Agricultural Techniques in 1974. Photo by Ricard Matzen. Source: [13]</span></p>
<p>Second, converting wind or solar energy directly into heat (or mechanical energy) can be more energy efficient than when electric conversion is involved. This means that less solar and wind energy converters – and thus less space and resources – are needed to supply a certain amount of heat. In short, the heat generating windmill addresses the main disadvantages of wind power: its low power density, and its <a href="https://www.lowtechmagazine.com/2017/09/how-to-run-modern-society-on-solar-and-wind-powe.html">intermittency</a>.</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">Mechanical windmills are less complex, which makes them more affordable and less resource-intensive to build, and which increases their lifetime</span></p>
</blockquote>
<p>Furthermore, direct heat generation greatly improves the economics and the sustainability of smaller types of windmills. Tests have shown that small wind turbines – producing electricity – are <a href="http://theoildrum.com.s3-website.us-east-2.amazonaws.com/node/6954">very inefficient and don’t always generate as much energy as was needed to produce them</a>. [<span style="color: #c00000;">12</span>] However, using similar models for heat production can decrease embodied energy and costs, increass lifetime, and improve efficiency.</p>
<h2 style="text-align: center;"><span style="color: #c00000;">How Much Heat Can a Windmill Produce?</span></h2>
<p>The Danish water brake windmill from the 1970s was a relatively small machine, with a rotor diameter of around 6 meters and a height of around 12 meters. Larger heat generating windmills were built in the 1980s. Most used simple wooden blades. In total, at least a dozen different models have been documented, both DIY and commercial models. [<span style="color: #c00000;">7</span>] Many were built with used car parts and other discarded materials. [<span style="color: #c00000;">13</span>]</p>
<p>One of the smaller early Danish heat generating windmills was officially tested. The Calorius type 37 – which had a rotor diameter of 5 meters and a height of 9 meters – produced 3.5 kilowatt of heat at a wind speed of 11 m/s (a strong breeze, Beaufort 6). This is comparable to the heat output of the smallest electric boilers for space heating. From 1993 to 2000, the Danish firm Westrup built a total of 34 water brake windmills based on this design, and by 2012 there were still 17 in operation. [<span style="color: #c00000;">7</span>]</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad39f5c4e200c-pi"><img class="asset asset-image at-xid-6a00e0099229e88833022ad39f5c4e200c img-responsive" style="width: 320px; display: block; margin-left: auto; margin-right: auto;" alt="Calorius-windmill" title="Calorius-windmill" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad39f5c4e200c-320wi" /></a></p>
<p style="text-align: center;"><span style="background-color: #ecdae5;">A Calorius windmill producing up to 4 kW of heat. Image provided by the <a href="http://www.folkecenter.eu">Nordic Folkecenter in Denmark</a>. </span>&nbsp;</p>
<p style="text-align: left;">A much larger water brake windmill (7.5m rotor diameter, 17m tower) was built in 1982 by the Svaneborg brothers, and heated the house of one of them (the other brother opted for a wind turbine and an electric heating system). The windmill, which had three fiberglass blades, produced up to 8 kilowatt of heat according to non-official measurements – comparable to the heat output of an electric boiler for a modest home. [<span style="color: #c00000;">7</span>]</p>
<p>Further into the 1980s, Knud Berthou built the most sophisticated heat generating windmill to date: the LO-FA. In other models, heat generation happened at the bottom of the tower – from the top of the windmill there was a shaft down to the bottom where the water brake was installed. However, in the LO-FA windmill all mechanical parts for energy conversion were moved to the top of the tower. The lower 10 meters of the 20 meter high tower were filled up with 15 tonnes of water in an insulated reservoir. Consequently, hot water could literally be tapped out of the windmill. [<span style="color: #c00000;">7</span>]</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">The tower of the LO-FA windmill was filled up with 15 tonnes of water in an insulated tank: hot water could literally be tapped out of the windmill.</span></p>
</blockquote>
<p>The LO-FA was also the largest of the heat generating windmills, with a 12 meter diameter rotor. Its heat output was estimated to be 90 kilowatt at a wind speed of 14 m/s (Beaufort 7). This results seems to be excessive compared to the other heat generating windmills, but the energy output of a windmill increases more than proportionally with the rotor diameter and the wind speed. Furthermore, the friction liquid in the water brake was not water but hydraulic oil, which can be heated up to much higher temperatures. The oil then transferred its heat to the water storage in the tower. [<span style="color: #c00000;">7</span>]</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Renewed Interest</span></h2>
<p>Interest in heat generating windmills resurfaced a few years ago, although for now it concerns only a handful of scientific studies. In a 2011 paper, German and UK scientists write that “small and remote households in northern regions demand thermal energy rather than electricity, and therefore wind turbines in such places should be build for thermal energy generation”. [<span style="color: #c00000;">8</span>]</p>
<p>The researchers explain and illustrate the workings of the water brake windmill, and calculate the optimal performance of the technology. It was found that the torque-speed characteristics of wind rotor and impeller should be carefully matched to achieve maximum efficiency. For example, for the very small Savonius windmill that the scientists used as a model (0.5m rotor diameter, 2m tower), it was calculated that the impeller diameter should be 0.388m.&nbsp;</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad39f1e9a200c-pi"><img class="asset asset-image at-xid-6a00e0099229e88833022ad39f1e9a200c img-responsive" style="width: 700px; display: block; margin-left: auto; margin-right: auto;" alt="heat production direct wind energy" title="heat production direct wind energy" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad39f1e9a200c-700wi" /></a></p>
<p>The researchers then ran simulations over a period of fifty hours to calculate the windmill’s heat output. Although the Savonius is a low speed windmill which is ill-suited for electricity generation, it turns out to be an excellent producer of heat: the small windmill produced up to 1 kW of thermal power (at wind speeds of 15 m/s). [<span style="color: #c00000;">8</span>] A 2013 study using a prototype obtained similar results, and calculated the efficiency of the system to be 91%. [<span style="color: #c00000;">9</span>] This is comparable to the efficiency of a wind turbine heating water through electricity.&nbsp;</p>
<blockquote>
<p style="text-align: right; padding-left: 120px;"><span style="font-size: 13pt;">A 2013 study using a prototype calculated the efficiency of the system to be 91%</span></p>
</blockquote>
<p>Obviously, it’s not always stormy weather, which means that the average wind speed is at least as important. A 2015 study investigates the possibilities of heat generating windmills in Lithuania, a Baltic country with a cold climate that’s dependent on expensive fuel imports. [<span style="color: #c00000;">14</span>] The researchers calculated that at the average wind speed in the country (4 m/s of Beaufort 3), generating one kilowatt of heat requires a windmill with a rotor diameter of 8.2 meters.</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3c53115200d-pi"><img class="asset asset-image at-xid-6a00e0099229e88833022ad3c53115200d img-responsive" alt="heat generating windmill 1975" title="heat generating windmill 1975" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3c53115200d-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p style="text-align: center;"><span style="background-color: #ecdae5;">A heat generating windmill with a water brake, placed inside the bottom of the tower. The mill was built by Jorgen Andersen in 1975, and stood in Serritslev. Photo by Claus Nybroe. Source: [13]</span></p>
<p>They compare this with the thermal energy demand of a 120 m2 energy efficient new building, heated to <a href="https://www.lowtechmagazine.com/2015/02/heating-people-not-spaces.html">modern comfort standards</a>, and conclude that a heat generating windmill could cover from 40-75% of the annual heating needs (depending on the energy efficiency class of the construction). [<span style="color: #c00000;">14</span>]</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Heat Storage</span></h2>
<p>The average wind speed is not guaranteed either, which means that a heat generating windmill requires heat storage – otherwise it would only provide heating when the wind blows. One cubic meter of heated water (1 ton, 1,000 liters) can hold up to 90 kWh of heat, which is roughly one to two days of supply for a household of four persons.</p>
<p><a class="asset-img-link" style="display: inline;" href="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3e522c5200b-pi"><img class="asset asset-image at-xid-6a00e0099229e88833022ad3e522c5200b img-responsive" alt="Thermal-windmill" title="Thermal-windmill" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3e522c5200b-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p style="text-align: center;"><span style="background-color: #ecdae5;">The same windmill as the one pictured above, seen from below. Source: [7]</span></p>
<p>Providing enough storage to bridge a week without wind thus requires up to 7 tonnes of water, which corresponds to a volume of 7 cubic meters plus insulation. However, energy losses (self-discharge) should also be taken into account, and this explains why the Danish heat generating windmills usually had a storage tank holding ten to twenty thousand liters of water. [<span style="color: #c00000;">13</span>]</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">A heat generating windmill can be combined with a solar boiler, so that both sun and wind can supply direct thermal energy using a smaller water tank.</span></p>
</blockquote>
<p>A heat generating windmill can also be combined with a solar boiler, so that both sun and wind can supply direct thermal energy using the same heat storage reservoir. In this case, it becomes possible to build a pretty reliable heating system with a smaller heat storage tank, because the combination of two – often complementary – energy sources increases the chances of direct heat supply. Especially in less sunny climates, heat generating windmills are a great addition to a solar thermal system, because the latter produces relatively less heat during winter, when heat demand is at its maximum.</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Retarders and Mechanical Heat Pumps</span></h2>
<p>The most recent and extensive studies to date are from 2016 and 2018, and compare different types of heat generating windmills with different types of indirect heat generation. [<span style="color: #c00000;">1</span>] [<span style="color: #c00000;">15</span>] In this second type of heat generating windmill, heat is produced with with mechanical heat pumps or hydrodynamic retarders, not with a water brake.</p>
<p>A mechanical heat pump is simply a heat pump without the electric motor – instead, the wind rotor is directly connected to the compressor(s) of the heat pump. This involves one less energy conversion, which makes the combination at least 10% more energy efficient than an electric heat pump driven by a wind turbine.</p>
<p>The hydrodynamic retarder is well known as a brake system in heavy vehicles. Like a joule machine, it converts rotational energy into heat without the involvement of electricity. Retarders and mechanical heat pumps have the same advantages as Joule Machines, in the sense that they are much smaller, lighter, and cheaper than electrical generators. However, in this case a gearbox is required to achieve optimal efficiency.</p>
<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad39f1ed2200c-pi"><img class="asset asset-image at-xid-6a00e0099229e88833022ad39f1ed2200c img-responsive" alt="direct versus indirect heat production wind" title="direct versus indirect heat production wind" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad39f1ed2200c-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p style="text-align: center;"><span style="background-color: #ecdae5;">Different types of direct and indirect heating production compared. Source: [15]</span></p>
<p>The study compares heat generating windmills based on retarders and mechanical heat pumps with indirect heat production using electric boilers and electric heat pumps. It compares these four technologies for three system sizes: a small windmill aimed at heating an off-the-grid household, a large windmill aimed at supplying heat to a village, and a wind farm producing heat for 20,000 inhabitants. The four heating concepts are ranked based on their yearly capital and operational expenditures, assuming a lifespan of 20 years. [<span style="color: #c00000;">1</span>] [<span style="color: #c00000;">15</span>]&nbsp;</p>
<blockquote>
<p style="text-align: right; padding-left: 40px;"><span style="font-size: 13pt;">Directly coupling a mechanical windmill to a mechanical heat pump is cheaper than using a gas boiler or the combination of a wind turbine and an electric heat pump.</span></p>
</blockquote>
<p>For the off-grid system, directly coupling a mechanical windmill to a mechanical heat pump is the cheapest option, while the combination of a wind turbine and an electric boiler is two to three times more expensive. All other technologies are in between. Taking into account both investment and operational costs, small-scale heat generating windmills with mechanical heat pumps are equally expensive or cheaper than conventional gas boilers when assuming the typical performance of a small windmill (which produces – over a period of one year – 12% to 22% of its maximum energy output).</p>
<p><a class="asset-img-link" style="display: inline;" href="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3e522e5200b-pi"><img class="asset asset-image at-xid-6a00e0099229e88833022ad3e522e5200b img-responsive" alt="Thermal-windmill3" title="Thermal-windmill3" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3e522e5200b-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p style="text-align: center;"><span style="background-color: #ecdae5;">Image: Water brake windmill developed by O. Helgason (left), water brake with variable load system (right). Images from “Test at very high wind speed of a windmill controlled by a water brake”, O. Helgason and&nbsp;<span class="caps">A.S.</span> Sigurdson, Science Institute, University of Iceland. Source: [7]</span></p>
<p>On the other hand, the combination of a small wind turbine and an electric heat pump requires a windmill with a “capacity factor” of at least 30% to become cost-competitive with gas heating – but such high performance is very unusual. Larger systems present the same rankings – the combination of mechanical windmills and mechanical heat pumps is the cheapest option – but they have up to three times lower capital costs due to economies of scale. Larger windmills have higher capacity factors (16-40%), which result in even larger cost savings.</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">Due to the large energy losses for heat transportation, the heat generating windmill is at its best as a decentralised energy source, providing heat to an off-the-grid household or – in the optimal case – a small city.</span></p>
</blockquote>
<p>However, larger systems also reveal a problem when scaling up the technology: storing heat may be cheaper and more efficient than storing electricity, but the opposite holds true for transportation: the energy losses for heat transportation are much larger than the energy losses for electricity transmission. The scientists calculate that the maximum distance that is cost-achievable under optimal wind conditions is 50 km. [<span style="color: #c00000;">15</span>]</p>
<p>Consequently, the heat generating windmill is at its best as a decentralised energy source, providing heat to an off-the-grid household or – in the optimal case – a relatively small town or city, or an industrial area. For even larger systems, energy needs to be transported in the form of electricity, and in that case direct generation of heat – with all its benefits – becomes unattractive.</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Blinded by Electricity</span></h2>
<p>Heat generating windmills are also investigated for renewable electricity production, mainly because they offer a better solution for energy storage <a href="https://www.lowtechmagazine.com/2015/05/sustainability-off-grid-solar-power.html">compared to batteries or other common technologies</a>. [<span style="color: #c00000;">16</span>] In these systems, the generated heat is converted to electricity by the use of a steam turbine. The storage system is similar to that of a concentrated solar power plant (CSP), and the solar concentrators are replaced by heat generating windmills.</p>
<p><a class="asset-img-link" style="display: inline;" href="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3c5315d200d-pi"><img class="asset asset-image at-xid-6a00e0099229e88833022ad3c5315d200d img-responsive" alt="Eddy current heater sobor" title="Eddy current heater sobor" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833022ad3c5315d200d-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p style="text-align: center;"><span style="background-color: #ecdae5;">An "eddy current heater". Source: [9]</span></p>
<p>Because high temperatures are needed to produce electricity efficiently with a steam turbine, these systems can’t make use of joule machines or hydrodynamic retarders, but instead rely on a type of retarder called an “eddy current heater” (or “induction heater”). These are comprised of a magnet mounted on a rotating shaft, and can reach temperatures of up to 600 degrees Celsius. Using eddy current heaters, windmills could provide direct heat at higher temperatures, making their potential use in industry even larger.&nbsp;</p>
<p>However, using the stored heat for electricity production is considerably more costly and less sustainable compared to using heat generating windmills for direct heat production. Converting the stored heat into electricity is at most 30% efficient, meaning that two thirds of the wind energy is lost due to needless energy conversions -- and the same is true <a href="https://www.lowtechmagazine.com/2011/07/solar-powered-factories.html">when solar thermal is used for power production</a>. [<span style="color: #c00000;">15</span>]</p>
<p>Direct heat production thus offers the possibility to save three times more greenhouse gas emissions and fossil fuels using the same number of windmills, which are also cheaper and more sustainable to build. Hopefully, direct heat production will be given the priority it deserves. Despite a warming climate, the demand for thermal energy is as high as ever.</p>
<p>Kris De Decker</p>
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<li><a href="https://www.lowtechmagazine.com/2015/02/heating-people-not-spaces.html">Restoring the old way of warming: heating people, not places</a></li>
<li><a href="https://www.lowtechmagazine.com/2013/08/direct-hydropower.html">Back to basics: direct hydro-power</a></li>
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<hr />
<h1>Sources:</h1>
<ol>
<li>Nitto, Dipl-Ing Alejandro Nicolás, Carsten Agert, and Yvonne Scholz. "<a href="https://elib.dlr.de/103317/1/20160224%20-%20Master%20Thesis_NITTO.pdf">WIND POWERED THERMAL ENERGY SYSTEMS (WTES)</a>".</li>
<li><a href="https://www.grin.com/document/384572">Integration of Thermal Energy Storage into Energy Network</a>, Sharyar Ahmed, 2017</li>
<li><a href="https://www.lowtechmagazine.com/2011/07/solar-powered-factories.html">The bright future of solar thermal powered factories</a>, Kris De Decker, Low-tech Magazine, 2011</li>
<li><a href="https://www.iea-shc.org/Data/Sites/1/publications/Solar-Heat-Worldwide-2018.pdf">Solar Heat Worldwide</a>, edition 2018, International Energy Agency (IEA).&nbsp;</li>
<li><a href="https://www.iea.org/renewables2018/heat/">Renewables 2018, Heat</a>, International Energy Agency (IEA).&nbsp;</li>
<li><a href="https://data.worldbank.org/indicator/EG.ELC.RNEW.ZS">World Bank: Renewable electricity output</a>.&nbsp;&nbsp;</li>
<li><em>The Rise of Modern Wind Energy: Wind Power for the World</em>. Pan Stanford Publishing, 2013. See chapter 13 ("Water brake windmills", Jørgen Krogsgaard) and chapter 16 ("Consigned to Oblivion", Preben Maegaard). These seem to be the only English language documents on Danish water brake windmills.</li>
<li>Chakirov, Roustiam, and Yuriy Vagapov. "<a href="http://www.ipcbee.com/vol19/3-ICECS2011R00007.pdf">Direct conversion of wind energy into heat using joule machine.</a>"&nbsp;<em>Fourth International Conference on Environmental and Computer Science (ICECS 2011), Singapore, Sept</em>. 2011.</li>
<li><a href="http://www.bulipi-eee.tuiasi.ro/archive/2013/fasc.4/p12_f4_2013.pdf">SMALL WIND ENERGY SYSTEM WITH PERMANENT MAGNET EDDY CURRENT HEATER</a>, BY ION SOBOR, VASILE RACHIER, ANDREI CHICIUC and RODION CIUPERCĂ. BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI. Publicat de Universitatea Tehnică „Gheorghe Asachi” din Iaşi Tomul LIX (LXIII), Fasc. 4, 2013</li>
<li><a href="http://diposit.ub.edu/dspace/bitstream/2445/67342/1/TFG-Pou-Gallo-Marcos.pdf">Joule’s experiment: An historico-critical approach</a>, Marcos Pou Gallo Advisor.</li>
<li>Okazaki, Toru, Yasuyuki Shirai, and Taketsune Nakamura. "<a href="https://www.sciencedirect.com/science/article/pii/S0960148115003079">Concept study of wind power utilizing direct thermal energy conversion and thermal energy storage</a>."&nbsp;<em>Renewable energy</em>&nbsp;83 (2015): 332-338.</li>
<li><a href="http://theoildrum.com.s3-website.us-east-2.amazonaws.com/node/6954">Real-world tests of small wind turbines in Netherlands and the UK</a>, Kris De Decker, The Oil Drum, 2010.</li>
<li><a href="http://windsofchange.dk/WOC-selfbuilders.php">Selfbuilders</a>, Winds of Change website, Erik Grove-Nielsen.</li>
<li>Černeckienė, Jurgita, and Tadas Ždankus. "<a href="https://www.researchgate.net/profile/Jurgita_Cerneckiene/publication/277568122_Usage_of_the_Wind_Energy_for_Heating_of_the_Energy-Efficient_Buildings_Analysis_of_Possibilities/links/5669301f08ae9da364ba0534.pdf">Usage of the Wind Energy for Heating of the Energy-Efficient Buildings: Analysis of Possibilities</a>."&nbsp;<em>Journal of Sustainable Architecture and Civil Engineering</em>&nbsp;10.1 (2015): 58-65.</li>
<li>Cao, Karl-Kiên, et al. "<a href="https://www.researchgate.net/publication/327508878_Expanding_the_horizons_of_power-to-heat_Cost_assessment_for_new_space_heating_concepts_with_Wind_Powered_Thermal_Energy_Systems">Expanding the horizons of power-to-heat: Cost assessment for new space heating concepts with Wind Powered Thermal Energy Systems</a>."&nbsp;<em>Energy</em>&nbsp;164 (2018): 925-936.</li>
<li>Okazaki, Toru, Yasuyuki Shirai, and Taketsune Nakamura. "<a href="https://www.sciencedirect.com/science/article/pii/S0960148115003079">Concept study of wind power utilizing direct thermal energy conversion and thermal energy storage</a>."&nbsp;<em>Renewable energy</em>&nbsp;83 (2015): 332-338.</li>
</ol>
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<p><a class="asset-img-link" href="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a477518b200d-pi"><img class="asset asset-image at-xid-6a00e0099229e888330240a477518b200d img-responsive" style="width: 720px; display: block; margin-left: auto; margin-right: auto;" alt="Lowtech-book-2012-2018" title="Lowtech-book-2012-2018" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330240a477518b200d-750wi" /></a></p>
<p>Low-tech Magazine makes the jump from web to paper. The first result is a&nbsp;<a href="http://www.lulu.com/shop/kris-de-decker/low-tech-magazine-20122018/paperback/product-24028679.html">710-page perfect-bound paperback</a>&nbsp;which is printed on demand and contains 37 of the most recent articles from the website (2012 to 2018). A second volume, collecting articles published between 2007 and 2011, will appear later this year.</p>
<p><span style="font-size: 18pt;"><strong><a href="https://www.lowtechmagazine.com/2019/03/printed-website.html">Read more: Low-tech Magazine: The Printed Website</a></strong>.&nbsp;</span></p>
<hr /></div>
Ditch the Batteries: Off-Grid Compressed Air Energy Storagetag:typepad.com,2003:post-6a00e0099229e888330224df322e9f200b2018-05-16T02:18:42+02:002019-02-25T22:43:54+01:00Going off-grid? Think twice before you invest in a battery system. Compressed air energy storage is the sustainable and resilient alternative to batteries, with much longer life expectancy, lower life cycle costs, technical simplicity, and low maintenance. Designing a compressed air energy storage system that combines high efficiency with small storage size is not self-explanatory, but a growing number of researchers show that it can be done. Compressed Air Energy Storage (CAES) is usually regarded as a form of large-scale energy storage, comparable to a pumped hydropower plant. Such a CAES plant compresses air and stores it in an underground cavern, recovering the energy by expanding (or decompressing) the air through a turbine, which runs a generator. Unfortunately, large-scale CAES...kris de decker
<div xmlns="http://www.w3.org/1999/xhtml"><p><a class="asset-img-link" style="display: inline;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330224e0391880200d-pi"><img class="asset asset-image at-xid-6a00e0099229e888330224e0391880200d img-responsive" alt="Diy compressed air" title="Diy compressed air" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224e0391880200d-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p>Going off-grid? Think twice before you invest in a battery system. Compressed air energy storage is the sustainable and resilient alternative to batteries, with much longer life expectancy, lower life cycle costs, technical simplicity, and low maintenance. Designing a compressed air energy storage system that combines high efficiency with small storage size is not self-explanatory, but a growing number of researchers show that it can be done.</p>
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<p>&nbsp;</p>
<p>Compressed Air Energy Storage (CAES) is usually regarded as a form of large-scale energy storage, comparable to a pumped hydropower plant. Such a CAES plant compresses air and stores it in an underground cavern, recovering the energy by expanding (or decompressing) the air through a turbine, which runs a generator.</p>
<p>Unfortunately, large-scale CAES plants are very energy inefficient. Compressing and decompressing air introduces energy losses, resulting in an electric-to-electric efficiency of only 40-52%, compared to 70-85% for pumped hydropower plants, and 70-90% for chemical batteries.</p>
<p>The low efficiency is mainly since air heats up during compression. This waste heat, which holds a large share of the energy input, is dumped into the atmosphere. A related problem is that air cools down when it is decompressed, lowering electricity production and possibly freezing the water vapour in the air. To avoid this, large-scale CAES plants heat the air prior to expansion using natural gas fuel, which further deteriorates the system efficiency and makes renewable energy storage dependent on fossil fuels.</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Why Small-scale CAES?</span></h2>
<p>In the previous article, we outlined several ideas – <a href="http://www.lowtechmagazine.com/2018/05/history-and-future-of-the-compressed-air-economy.html">inspired by historical systems</a>&nbsp;– that could improve the efficiency of large-scale CAES plants. In this article, we focus on the small but growing number of engineers and researchers who think that the future is not in large-scale compressed air energy storage, but rather in small-scale or micro systems, using man-made, aboveground storage vessels instead of underground reservoirs. Such systems could be off-the-grid or grid-connected, either operating by themselves or alongside a battery system.</p>
<p>The main reason to investigate decentralised compressed air energy storage is the simple fact that such a system could be installed anywhere, just like chemical batteries. Large-scale CAES, on the other hand, is dependent on a suitable underground geology. Although there are more potential sites for large-scale CAES plants than for large-scale pumped hydropower plants, finding appropriate storage caverns is not as easy as was previously assumed. [<span style="background-color: #ffffff; color: #c00000;">1</span>-<span style="color: #c00000;">2</span>] [<span style="color: #00bf00;">3</span>]</p>
<p><a class="asset-img-link" style="display: inline;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03a0631200d-pi"><img class="asset asset-image at-xid-6a00e0099229e888330224e03a0631200d img-responsive" alt="Set up small scale compressed air energy storage system" title="Set up small scale compressed air energy storage system" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03a0631200d-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p style="text-align: center;">Experimental set-up of small-scale compressed air energy storage system. Source: [27]</p>
<p>Compared to chemical batteries, micro-CAES systems have some interesting advantages. Most importantly, a distributed network of compressed air energy storage systems would be much more sustainable and environmentally friendly. Over their lifetimes, <a href="http://www.lowtechmagazine.com/2015/05/sustainability-off-grid-solar-power.html">chemical batteries store only two to ten times the energy needed to manufacture them</a>. [<span style="color: #c00000;">4</span>] Small-scale CAES systems do much better than that, mainly because of their much longer lifespan.</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">Compared to chemical batteries, a distributed network of compressed air energy storage systems would be much more sustainable and environmentally friendly</span></p>
</blockquote>
<p>Furthermore, they do not require rare or toxic materials, and the hardware is easily recyclable. In addition, decentralised compressed air energy storage doesn’t need high-tech production lines and can be manufactured, installed and maintained by local business, unlike an energy storage system based on chemical batteries. Finally, micro-CAES has no self-discharge, is tolerant of a wider range of environments, and promises to be cheaper than chemical batteries. [<span style="color: #c00000;">5</span>]</p>
<p><a class="asset-img-link" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330224df331733200b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330224df331733200b img-responsive" style="width: 400px; display: block; margin-left: auto; margin-right: auto;" alt="Sustainability storage options barnhart 2013" title="Sustainability storage options barnhart 2013" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224df331733200b-400wi" /></a></p>
<p>Although the initial investment cost is estimated to be higher than that of a battery system (around $10,000 for a typical residential set-up), and although above-ground storage increases the costs in comparison to underground storage (the storage vessel is good for roughly half of the investment cost), a compressed air energy storage system offers an almost infinite number of charge and discharge cycles. Batteries, on the other hand, need to be replaced every few years, which makes them more expensive in the long run. [<span style="color: #c00000;">5</span>,<span style="color: #c00000;">6</span>]</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Challenge: Limiting Storage Size</span></h2>
<p>However, decentralised CAES also faces important challenges. The first is the system efficiency, which is a problem in large- and small-scale systems alike, and the second is the size of the storage vessel, which is especially problematic for small-scale CAES systems.</p>
<p>Both issues make small-scale CAES systems unpractical. Sufficient space for a large storage vessel is not always available, while a low storage efficiency requires a larger solar PV or wind power plant to make up for that loss, raising the costs and lowering the sustainability of the system.</p>
<p>To make matters worse, system efficiency and storage size are inversely related: improving one factor is often at the expense of the other. Increasing the air pressure minimizes the storage size but decreases the system efficiency, while using a lower pressure makes the system more energy efficient but results in a larger storage size. Some examples help illustrate the problem.</p>
<p><a class="asset-img-link" style="display: inline;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03a054c200d-pi"><img class="asset asset-image at-xid-6a00e0099229e888330224e03a054c200d img-responsive" alt="Compressed air tanks" title="Compressed air tanks" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03a054c200d-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p style="text-align: center;"><a class="asset-img-link" style="display: inline;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330224df33149f200b-pi"></a>Compressed air energy storage tanks. <a href="http://www.screwtypeaircompressors.com/sale-8108163-vertical-compressed-air-tank-natural-gas-tank-2000l-air-receiver-tank.html" target="_blank" rel="noopener noreferrer">Source</a>.&nbsp;</p>
<p>A simulation for a stand-alone CAES aimed at unpowered rural areas, and which is connected to a solar PV system and used for lighting only, operates at a relatively low air pressure of 8 bar and obtains a round-trip efficiency of 60% -- comparable to the efficiency of lead-acid batteries. [<span style="color: #c00000;">7</span>]</p>
<p>However, to store 360 Wh of potential electrical energy, the system requires a storage reservoir of 18 m3, the size of a small room measuring 3x3x2 metres. The authors note that “although the tank size appears very large, it still makes sense for applications in rural areas”.</p>
<blockquote>
<p style="text-align: right; padding-left: 30px;"><span style="font-size: 13pt;">System efficiency and storage size are inversely related: improving one factor is often at the expense of the other.</span></p>
</blockquote>
<p>Such a system may indeed be beneficial in this context, especially because it has a much longer lifespan than chemical batteries. However, a similar configuration in an urban context with high energy use is obviously problematic. In another study, it was calculated that it would take a 65 m3 air storage tank to store 3 kWh of energy. This corresponds to a 13 metre long pressure vessel with a diameter of 2.5 metres, shown below. [<span style="color: #c00000;">8</span>]</p>
<p><img class="asset asset-image at-xid-6a00e0099229e888330224e03919cd200d img-responsive" alt="Air receiver" title="Air receiver" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03919cd200d-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></p>
<p>Furthermore, average household electricity use per day in industrialised countries is much higher still. For example, in the UK it’s slightly below 13 kWh per day, in the US and Canada it’s more than 30 kWh. In the latter case, ten such air pressure tanks would be required to store one day of electricity use.</p>
<p>Small-scale CAES systems with high pressures give the opposite results. For example, a configuration modelled for a typical household electrical use in Europe (6,400 kWh per year) operates at a pressure of 200 bar (almost 4 times higher than the pressure in large-scale CAES plants) and achieves a storage volume of only 0.55 m3, which is comparable to batteries. However, the electric-to-electric efficiency of this set-up is only 11-17%, depending on the size of the solar PV system. [<span style="color: #c00000;">9</span>]</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Two Strategies to Make Micro CAES work</span></h2>
<p>These examples seem to suggest that compressed air energy storage makes no sense as a small-scale energy storage system, <a href="http://www.lowtechmagazine.com/2018/01/how-much-energy-do-we-need.html">even with a reduction in energy demand</a>. However, perhaps surprisingly to many, this is not the case.</p>
<p>Small-scale CAES systems cannot follow the same approach as large-scale CAES systems, which increase storage capacity and overall efficiency by using multi-stage compression with intercooling and multi-stage expansion with reheating. This method involves additional components and increases the complexity and cost, which is impractical for small-scale systems.</p>
<p><img class="asset asset-image at-xid-6a00e0099229e888330224e03a0506200d img-responsive" alt="Elevated 2" title="Elevated 2" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03a0506200d-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></p>
<p>The same goes for “adiabatic” processes (AA-CAES), which aim to use the heat of compression to reheat the expanding air, and which are the main research focus for large-scale CAES. For a micro-CAES system, it’s very important to simplify the structure as much as possible. [<span style="color: #c00000;">5</span>,<span style="color: #c00000;">10</span>]</p>
<p>This leaves us with two low-tech strategies that can be followed to achieve similar storage capacity and energy efficiency as lead-acid batteries. First, we can design low pressure systems which minimize the temperature differences during compression and expansion. Second, we can design high pressure systems in which the heat and cold from compression and expansion are used for household applications.</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Small-scale, High Pressure</span></h2>
<p>Small-scale compressed air energy storage systems with high air pressures turn the inefficiency of compression and expansion into an advantage. While large-scale AA-CAES aims to recover the heat of compression with the aim of maximizing electricity production, these small-scale systems take advantage of the temperature differences to allow trigeneration of electrical, heating and cooling power. The dissipated heat of compression is used for residential heating and hot water production, while the cold expanding air is used for space cooling and refrigeration. Chemical batteries can’t do this.</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">Small-scale, high pressure systems use the dissipated heat of compression for residential heating and hot water production, while the cold expanding air is used for space cooling and refrigeration.</span></p>
</blockquote>
<p>In these systems, the electric-to-electric efficiency is very low. However, there are now several efficiencies to define, because the system also supplies heat and cold. [<span style="color: #c00000;">10</span>,<span style="color: #c00000;">11</span>] Furthermore, this approach can make several electrical appliances unnecessary, such as the refrigerator, the air-conditioning, and the electric boiler for space and water heating. Since the use of these appliances is often responsible for roughly half of the electricity use in an average household, a small-scale CAES system with high pressure has lower electricity demand overall.</p>
<p style="text-align: center;"><a class="asset-img-link" style="display: inline;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330224df3314cb200b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330224df3314cb200b img-responsive" alt="Air compressor" title="Air compressor" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224df3314cb200b-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a>A typical air compressor. <a href="https://www.thomasnet.com/articles/machinery-tools-supplies/Air-Compressors" target="_blank" rel="noopener noreferrer">Source</a>.</p>
<p>High pressure systems easily solve the issue of storage size. As we have seen, a higher air pressure can greatly reduce the size of a compressed air storage vessel, but only at the expense of increased waste heat. In a small-scale system that takes advantage of temperature differences to provide heating and cooling, this is advantageous. Therefore, high pressure systems are ideal for small-scale residential buildings, where storage space is limited and where there is a large demand for heat and cold as well as electricity. The only disadvantages are that high pressure systems require stronger and more expensive storage tanks, and that extra space is required for heat exchangers.</p>
<p><img class="asset asset-image at-xid-6a00e0099229e888330224e03a05a0200d img-responsive" alt="Experiment set up Sun 2015" title="Experiment set up Sun 2015" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03a05a0200d-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></p>
<p style="text-align: center;">Experimental set-up of a micro CAES system. Source: [30]</p>
<p>Several research groups have designed, modeled and built small-scale combined heat-and-power CAES units which provide heating and cooling as well as electricity. The high pressure system with a storage volume of only 0.55 m3 that we mentioned earlier, is an example of this type of system. [<span style="color: #c00000;">9</span>] As noted, its electrical efficiency is only 11-17%, but the system also produces sufficient heat to produce 270 litres of hot water per day. If this thermal source of energy is also taken into account, the “exergetic” efficiency of the whole system is close to 70%. Similar "<a href="https://en.wikipedia.org/wiki/Exergy" target="_blank" rel="noopener noreferrer">exergy</a>" efficiencies can be found in other studies, with systems operating at pressures between 50 and 200 bar. [<span style="color: #c00000;">11</span>-<span style="color: #c00000;">21</span>]</p>
<p>Heat and cold from compression and expansion can be distributed to heating or cooling devices by means of water or air. The setup of an air cycle heating and cooling system is very similar to a CAES system, except for the storage vessel. Air cycle heating and cooling has many advantages, including high reliability, ease of maintenance, and the use of a natural refrigerant, which is environmentally benign. [<span style="color: #c00000;">11</span>]</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Small-scale, Low Pressure</span></h2>
<p>The second strategy to achieve higher efficiencies and lower storage volumes is exactly the opposite from the first. Instead of compressing air to a high pressure and taking advantage of the heat and cold from compression and expansion, a second class of small-scale CAES systems is based on low pressures and “near-isothermal” compression and expansion.</p>
<p>Below air pressures of roughly 10 bar, the compression and expansion of air exhibit insignificant temperature changes (“near-isothermal”), and the efficiency of the energy storage system can be close to 100%. There is no waste heat and consequently there is no need to reheat the air upon expansion.&nbsp;</p>
<p style="text-align: center;"><a class="asset-img-link" style="display: inline;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330223c84b62b6200c-pi"><img class="asset asset-image at-xid-6a00e0099229e888330223c84b62b6200c img-responsive" alt="Hiscox three stage compressor edited" title="Hiscox three stage compressor edited" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330223c84b62b6200c-500wi" /></a></p>
<p>Isothermal compression requires the least amount of energy to compress a given amount of air to a given pressure. However, reaching an isothermal process is far from reality. To start with, it only works with small and/or slowly cycling compressors and expanders. Unfortunately, typical industrial compressors are not made for maximum efficiency but for maximum power and thus work under fast-cycling, non-isothermal conditions. The same goes for most industrial expanders. [<span style="color: #c00000;">22</span>-<span style="color: #c00000;">24</span>]</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">Below air pressures of 10 bar, compression and expansion of air exhibit insignificant temperature changes and the efficiency can be close to 100%. </span></p>
</blockquote>
<p>The use of industrial compressors and expanders explains in large part why the low pressure CAES systems mentioned at the beginning of this article have such large storage vessels. Both systems are based on devices which are operated outside of their optimal or rated conditions. [<span style="color: #00bf00;">25</span>] Because inefficiencies multiply during energy conversions, even relatively small differences in the efficiency of compressors and expanders can have large effects. For example, a variation in device efficiency from 60% to 80% results in a system efficiency from 36% to 64%, respectively.</p>
<h2 style="text-align: center;"><span style="color: #c00000;">New Types of Compressors and Expanders</span></h2>
<p>Because the performance of a compressor and an expander significantly impact the overall efficiency of a small-scale CAES system, several researchers have built their own compressors and expanders, which are especially aimed at energy storage. For example, one team designed, built and examined a single-stage, low power isothermal compressor that uses a liquid piston. [<span style="color: #c00000;">22</span>] It operates at a very low compression rate (between 10-60 rpm), which correspond to the output of solar PV panels, and limits temperature fluctuation during compression and expansion to 2 degrees Celsius.</p>
<p>The low-cost device has minimum moving parts and obtains efficiencies of 60-70% at 3 to 7 bar pressure. [<span style="color: #c00000;">22</span>] This is a very high efficiency for such a simple device, considering that a sophisticated three-stage centrifugal compressor, used in large-scale CAES systems or in industrial settings, is roughly 70% efficient. Furthermore, the researchers state that the efficiency is limited by the off-the-shelf motor that they use to power their compressor. Indeed, another research team achieved 83% efficiency. [<span style="color: #c00000;">26</span>]</p>
<p><img class="asset asset-image at-xid-6a00e0099229e888330224e03919d4200d img-responsive" alt="Scroll compressor Sun 2015" title="Scroll compressor Sun 2015" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03919d4200d-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></p>
<p style="text-align: center;">A scroll compressor. Source: [30]</p>
<p>Another novelty is the use of scroll compressors, which are the types of compressors that are now used in refrigerators, air-conditioning systems, and heat pumps. Both fluid piston and scroll compressors have a high area-to-volume ratio, which minimizes heat production, and can easily handle two-phase flow, which means that they can also be used as expanders. They are also lighter and less noisy than typical reciprocating compressors. [<span style="color: #c00000;">24</span>]</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Varying Air Pressure</span></h2>
<p>Although compressors and expanders are the most important determinants of system efficiency in small-scale CAES systems, they are not the only ones. For example, in every compressed air energy storage system, additional efficiency loss is caused by the fact that during expansion the storage reservoir is depleted and therefore the pressure drops. Meanwhile, the input pressure for the expander is required to vary only in a minimal range to assure high efficiency.</p>
<p><a class="asset-img-link" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330224df331749200b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330224df331749200b img-responsive" style="width: 200px; display: block; margin-left: auto; margin-right: auto;" alt="Air pressure gauge" title="Air pressure gauge" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224df331749200b-200wi" /></a></p>
<p>This is usually solved in two ways, although neither is really satisfactory. First, air can be stored in a tank with surplus pressure, after which it is throttled down to the required expander input pressure. However, this method – which is used in large-scale CAES – requires additional energy use and thus introduces inefficiency. Second, the expander can operate at variable conditions, but in this case efficiency will drop along with the pressure while the storage is emptied.</p>
<blockquote>
<p style="text-align: right; padding-left: 90px;"><span style="font-size: 13pt;">During expansion the storage reservoir is depleted and therefore the pressure drops.</span></p>
</blockquote>
<p>With these problems in mind, a team of researchers combined a small-scale CAES with a small-scale pumped hydropower plant, resulting in a system that maintains a steady pressure during the complete discharge of the storage reservoir. It consists of two compressed air tanks that are connected by a pipe attached to their lower portions: each of these have separate spaces for air (below) and water storage (above). The configuration maintains a head of water by means of a pump, which consumes 15% of the generated power. However, in spite of this extra energy use, the researchers managed to increase both the efficiency and the energy density of the system. [<span style="color: #c00000;">11</span>]</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Off-the-Grid Power Storage</span></h2>
<p>To give an idea of what a combination of the right components can achieve, let’s have a look at a last research project. [<span style="color: #c00000;">27</span>] It concerns a system that is based on a highly efficient, custom-made compressor/expander, which is directly coupled to a DC motor/generator. Apart from its efficient components, this CAES project also introduces an innovative system configuration. It doesn’t use one large air storage tank, but several smaller ones, which are interconnected and computer-controlled.</p>
<p>The setup consists of the compression/expansion unit coupled to three small (7L) cylinders, previously used as air extinguishers, and operates at low pressure (max 5 bar). The storage vessels are connected via PVC pipework and brass fittings. To control the air-flow, three computer-controlled air valves are installed at the inlet of each cylinder. The system can be extended by adding more pressure vessels. [<span style="color: #c00000;">27</span>]</p>
<p><a class="asset-img-link" style="display: inline;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330223c84a8018200c-pi"><img class="asset asset-image at-xid-6a00e0099229e888330223c84a8018200c img-responsive" alt="Small scale caes setup" title="Small scale caes setup" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330223c84a8018200c-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p>A modular configuration results in a higher system efficiency and energy density for mainly two reasons. First, it helps more effective heat transfer to take place, because every air tank acts as an additional heat exchanger. Second, it allows better control over the discharge rate of the storage reservoir. The cylinders can be discharged either in unison to satisfy a demand for high power density (more power at the cost of a shorter discharge time), or they can be discharged sequentially to satisfy a demand for high energy density (longer discharge time at the cost of maximum power).</p>
<blockquote>
<p style="text-align: right; padding-left: 30px;"><span style="font-size: 13pt;">By discharging modular storage cylinders sequentially, the discharge time can be greatly increased, making the system comparable to lead-acid batteries in terms of energy density.</span>&nbsp;</p>
</blockquote>
<p>By discharging the cylinders sequentially, the discharge time can be greatly increased, making the system comparable to lead-acid batteries in terms of energy density. Based on their experimental set-up, the researchers calculated the efficiencies for different starting pressures and numbers of cylinders. They found that 57 interconnected cylinders of 10 litre each, operating at 5 bar, could fulfill the job of four 24V batteries for 20 consecutive hours, all while having a surprisingly small footprint of just 0.6 m3.&nbsp;</p>
<p>Interestingly, the storage capacity is 410 Wh, which is comparable to the 360 Wh rural system noted earlier, which requires an 18 m3 storage vessel – that’s thirty times larger than the modular storage system.</p>
<p style="text-align: center;"><a class="asset-img-link" style="display: inline;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330224df331516200b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330224df331516200b img-responsive" alt="Computer controlled air valves" title="Computer controlled air valves" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224df331516200b-500wi" style="display: block; margin-left: auto; margin-right: auto;" /></a>Computer-controlled air valves. <a href="http://www.jaksa.si/compressed-air-solenoid-valves.html" target="_blank" rel="noopener noreferrer">Source</a>.</p>
<p>The electric-to-electric efficiency for the 3-cylinder set-up reached a peak of 85% at 3 bar pressure, while the estimated efficiency for the 57-cylinder set-up is 75%. These are values comparable to lithium-ion batteries, but adding more storage vessels or operating at higher pressures introduces larger losses due to compression, heat, friction and fittings. [<span style="color: #c00000;">27</span>-<span style="color: #c00000;">29</span>]</p>
<p>Nevertheless, when I e-mailed Abdul Alami, the main author of the study, thinking that the results sounded too good to be true, he told me that the figures were actually overly conservative: “We stuck to low pressures to achieve near-isothermal compression and to ensure safe operation. Operating at pressures higher than 10 bar would create serious thermal losses, but a pressure of 7-8 bar may be beneficial in terms of energy and power density, though maybe not in terms of efficiency.”</p>
<h2 style="text-align: center;"><span style="color: #c00000;">Build it Yourself?</span></h2>
<p>In conclusion, small-scale compressed air energy storage could be a promising alternative to batteries, but the research is still in its early stages – the first study on small-scale CAES was published in 2010 – and new ideas will continue to shed light on how best to develop the technology. At the moment, there are no commercial products available, and setting up your own system can be quite intimidating if you are new to pneumatics. Simply getting hold of the right components and fittings is a headache, as these come in a bewildering variety and are only sold to industries.</p>
<p>However, if you’re patient and not too unhandy, and if you are determined to use a more sustainable energy storage system, it is perfectly possible to build your own CAES system. As the examples in this article have shown, it’s just a bit harder to build a good one.</p>
<p>Kris De Decker</p>
<p>There's more ideas for small-scale CAES systems in the previous article: <a href="http://www.lowtechmagazine.com/2018/05/history-and-future-of-the-compressed-air-economy.html">History and Future of the Compressed Air Economy</a>.&nbsp;</p>
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<p><span style="font-size: 13pt;"><strong>References &amp; Notes:</strong></span></p>
<p>[1]&nbsp;Luo, Xing, et al. "Overview of current development in electrical energy storage technologies and the application potential in power system operation." <em>Applied Energy</em> 137 (2015): 511-536.&nbsp;<a href="https://www.sciencedirect.com/science/article/pii/S0306261914010290" target="_blank" rel="noopener noreferrer">https://www.sciencedirect.com/science/article/pii/S0306261914010290</a></p>
<p>[2]&nbsp;Laijun, C. H. E. N., et al. "Review and prospect of compressed air energy storage system."&nbsp;Journal of Modern Power Systems and Clean Energy&nbsp;4.4 (2016): 529-541. https://link.springer.com/article/10.1007/s40565-016-0240-5</p>
<p>[3]&nbsp;There is increasing competition for potential CAES geologic units, as many are also well suited to the storage of natural gas or sequestered carbon. Furthermore, cavern storage imposes harsh requirements on the geographical conditions. For example, the originally planned Iowa CAES project in the US was terminated due to its porous sandstone condition. [2]</p>
<p>[4]&nbsp;Barnhart, Charles J., and Sally M. Benson. "On the importance of reducing the energetic and material demands of electrical energy storage." <em>Energy &amp; Environmental Science</em> 6.4 (2013): 1083-1092.&nbsp;https://gcep.stanford.edu/pdfs/EES_reducingdemandsonenergystorage.pdf</p>
<p>[5]&nbsp;Petrov, Miroslav P., Reza Arghandeh, and Robert Broadwater. "Concept and application of distributed compressed air energy storage systems integrated in utility networks." <em>ASME 2013 Power Conference</em>. American Society of Mechanical Engineers, 2013.&nbsp;<a href="http://eddism.com/wp-content/uploads/2014/10/Paper-EDD-Concept-and-Application-of-Distributed-Compressed-Air-Energy-Storage-Systems-Integrated-in-Utility-Networks-July-2013.pdf" target="_blank" rel="noopener noreferrer">http://eddism.com/wp-content/uploads/2014/10/Paper-EDD-Concept-and-Application-of-Distributed-Compressed-Air-Energy-Storage-Systems-Integrated-in-Utility-Networks-July-2013.pdf</a></p>
<p>[6]&nbsp;Tallini, Alessandro, Andrea Vallati, and Luca Cedola. "Applications of micro-CAES systems: energy and economic analysis."&nbsp;Energy Procedia&nbsp;82 (2015): 797-804.</p>
<p>[7]&nbsp;Setiawan, A., et al. "Sizing compressed-air energy storage tanks for solar home systems." <em>Computational Intelligence and Virtual Environments for Measurement Systems and Applications (CIVEMSA), 2015 IEEE International Conference on</em>. IEEE, 2015.&nbsp;<a href="https://www.researchgate.net/profile/Ardyono_Priyadi/publication/274898992_Sizing_Compressed-Air_Energy_Storage_Tanks_for_Solar_Home_Systems/links/5670e2c408ae2b1f87acf927.pdf" target="_blank" rel="noopener noreferrer">https://www.researchgate.net/profile/Ardyono_Priyadi/publication/274898992_Sizing_Compressed-Air_Energy_Storage_Tanks_for_Solar_Home_Systems/links/5670e2c408ae2b1f87acf927.pdf</a></p>
<p>[8]&nbsp;Herriman, Kayne. "Small compressed air energy storage systems." (2013).&nbsp;<a href="https://eprints.usq.edu.au/24651/1/Herriman_2013.pdf" target="_blank" rel="noopener noreferrer">https://eprints.usq.edu.au/24651/1/Herriman_2013.pdf</a></p>
<p>[9]&nbsp;Manfrida, Giampaolo, and Riccardo Secchi. "Performance prediction of a small-size adiabatic compressed air energy storage system." <em>International Journal of Thermodynamics</em> 18.2 (2015): 111-119.&nbsp;<a href="http://dergipark.ulakbim.gov.tr/eoguijt/article/download/5000071710/5000113411" target="_blank" rel="noopener noreferrer">http://dergipark.ulakbim.gov.tr/eoguijt/article/download/5000071710/5000113411</a></p>
<p>[10]&nbsp;Kim, Y. M., and Daniel Favrat. "Energy and exergy analysis of a micro-compressed air energy storage and air cycle heating and cooling system." Energy 35.1 (2010): 213-220.</p>
<p>[11]&nbsp;Kim, Young Min. "Novel concepts of compressed air energy storage and thermo-electric energy storage." (2012).&nbsp;<a href="https://infoscience.epfl.ch/record/181540/files/EPFL_TH5525.pdf" target="_blank" rel="noopener noreferrer">https://infoscience.epfl.ch/record/181540/files/EPFL_TH5525.pdf</a></p>
<p>[12]&nbsp;Inder, Shane D., and Mehrdad Khamooshi. "Energy Efficiency Analysis of Discharge Modes of an Adiabatic Compressed Air Energy Storage System."&nbsp;World Academy of Science, Engineering and Technology, International Journal of Electrical, Computer, Energetic, Electronic and Communication Engineering&nbsp;11.12 (2017): 1101-1109.&nbsp;</p>
<p>[13]&nbsp;Vollaro, Roberto De Lieto, et al. "Energy and thermodynamical study of a small innovative compressed air energy storage system (micro-CAES)."&nbsp;Energy Procedia&nbsp;82 (2015): 645-651.</p>
<p>[14]&nbsp;Li, Yongliang, et al. "A trigeneration system based on compressed air and thermal energy storage."&nbsp;Applied Energy&nbsp;99 (2012): 316-323. <a href="https://www.sciencedirect.com/science/article/pii/S0306261912003479" target="_blank" rel="noopener noreferrer">https://www.sciencedirect.com/science/article/pii/S0306261912003479</a>&nbsp;</p>
<p>[15]&nbsp;Facci, Andrea L., et al. "Trigenerative micro compressed air energy storage: Concept and thermodynamic assessment."&nbsp;Applied energy&nbsp;158 (2015): 243-254. https://www.sciencedirect.com/science/article/pii/S0306261915009526&nbsp;</p>
<p>[16]&nbsp;Mohammadi, Amin, et al. "Exergy analysis of a Combined Cooling, Heating and Power system integrated with wind turbine and compressed air energy storage system."&nbsp;Energy Conversion and Management&nbsp;131 (2017): 69-78. https://www.sciencedirect.com/science/article/pii/S0306261915009526&nbsp;</p>
<p>[17]&nbsp;Yao, Erren, et al. "Thermo-economic optimization of a combined cooling, heating and power system based on small-scale compressed air energy storage." Energy Conversion and Management&nbsp;118 (2016): 377-386. https://www.sciencedirect.com/science/article/pii/S0196890416302229&nbsp;</p>
<p>[18]&nbsp;Liu, Jin-Long, and Jian-Hua Wang. "Thermodynamic analysis of a novel tri-generation system based on compressed air energy storage and pneumatic motor."&nbsp;Energy&nbsp;91 (2015): 420-429. https://www.sciencedirect.com/science/article/pii/S0360544215011317&nbsp;</p>
<p>[19]&nbsp;Lv, Song, et al. "Modelling and analysis of a novel compressed air energy storage system for trigeneration based on electrical energy peak load shifting."&nbsp;Energy Conversion and Management&nbsp;135 (2017): 394-401. https://www.sciencedirect.com/science/article/pii/S0196890416311839&nbsp;</p>
<p>[20]&nbsp;Besharat, M. O. H. S. E. N., SANDRA C. Martins, and HELENA M. Ramos. "Evaluation of Energy Recovery in Compressed Air Energy Storage (CAES) Systems."&nbsp;3rd IAHR Europe Congress. Book of Proceedings, Portugal. 2014. https://www.researchgate.net/profile/Mohsen_Besharat2/publication/270896130_Evaluation_of_Energy_Recovery_in_Compressed_Air_Energy_Storage_CAES_Systems/links/58a1fce0a6fdccf5e97109b2/Evaluation-of-Energy-Recovery-in-Compressed-Air-Energy-Storage-CAES-Systems.pdf&nbsp;</p>
<p>[21]&nbsp;Minutillo, M., A. Lubrano Lavadera, and E. Jannelli. "Assessment of design and operating parameters for a small compressed air energy storage system integrated with a stand-alone renewable power plant."&nbsp;Journal of Energy Storage&nbsp;4 (2015): 135-144. https://www.sciencedirect.com/science/article/pii/S2352152X15300207&nbsp;</p>
<p>[22]&nbsp;Villela, Dominique, et al. "Compressed-air energy storage systems for stand-alone off-grid photovoltaic modules." <em>Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE</em>. IEEE, 2010.&nbsp;<a href="https://pdfs.semanticscholar.org/9f1d/4273f8deb4a0a18c86eb4056e2fd378f8f3f.pdf" target="_blank" rel="noopener noreferrer">https://pdfs.semanticscholar.org/9f1d/4273f8deb4a0a18c86eb4056e2fd378f8f3f.pdf</a></p>
<p>[23]&nbsp;Paloheimo, H., and M. Omidiora. "A feasibility study on Compressed Air Energy Storage system for portable electrical and electronic devices."&nbsp;Clean Electrical Power, 2009 International Conference on. IEEE, 2009. <a href="https://www.researchgate.net/profile/Michael_Omidiora/publication/224581292_A_Feasibility_Study_on_Compressed_Air_Energy_Storage_System_for_Portable_Electrical_and_Electronic_Devices/links/5640d5d308aebaaea1f6ad44.pdf&nbsp;" target="_blank" rel="noopener noreferrer">https://www.researchgate.net/profile/Michael_Omidiora/publication/224581292_A_Feasibility_Study_on_Compressed_Air_Energy_Storage_System_for_Portable_Electrical_and_Electronic_Devices/links/5640d5d308aebaaea1f6ad44.pdf&nbsp;</a></p>
<p>[24] Prinsen, Thomas H. <em>Design and analysis of a solar-powered compressed air energy storage system</em>. Naval Postgraduate School Monterey United States, 2016. <a href="https://scholar.google.com/scholar?cluster=5783353621699682542&amp;hl=nl&amp;as_sdt=2005&amp;sciodt=0,5" target="_blank" rel="noopener noreferrer">https://scholar.google.com/scholar?cluster=5783353621699682542&amp;hl=nl&amp;as_sdt=2005&amp;sciodt=0,5</a></p>
<p><span style="background-color: #ffffff;">[25] The small-scale system aimed at urban environments, which has a storage reservoir of 18 metres long, is based on a compressor that “had been in service for 30 years on building sites to run various air tools and had little maintenance done”. [8] This is detrimental to system efficiency, because a compressor that is not maintained well easily wastes as much as 30% of its potential output through air leaks, increased friction, or dirty air filters. This small-scale system also used a highly inefficient expander. All together, this explains why it combines a very large storage volume with a very low electric-to-electric efficiency (less than 5%).</span></p>
<p><span style="background-color: #ffffff;">[26]&nbsp;Van de Ven, James D., and Perry Y. Li. "Liquid piston gas compression." <em>Applied Energy</em> 86.10 (2009): 2183-2191.&nbsp;<a href="https://experts.umn.edu/en/publications/liquid-piston-gas-compression" target="_blank" rel="noopener noreferrer">https://experts.umn.edu/en/publications/liquid-piston-gas-compression</a></span></p>
<p>[27]&nbsp;Alami, Abdul Hai, et al. "Low pressure, modular compressed air energy storage (CAES) system for wind energy storage applications." <em>Renewable Energy</em> 106 (2017): 201-211.</p>
<p>[28]&nbsp;Alami, Abdul Hai. "Experimental assessment of compressed air energy storage (CAES) system and buoyancy work energy storage (BWES) as cellular wind energy storage options." <em>Journal of Energy Storage</em> 1 (2015): 38-43.</p>
<p>[29] Abdul Alami, e-mail conversation.</p>
<p>[30] Sun, Hao, Xing Luo, and Jihong Wang. "Feasibility study of a hybrid wind turbine system–Integration with compressed air energy storage." <em>Applied Energy</em> 137 (2015): 617 -628. https://www.sciencedirect.com/science/article/pii/S0306261914006680</p>
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<p>Low-tech Magazine makes the jump from web to paper. The first result is a&nbsp;<a href="http://www.lulu.com/shop/kris-de-decker/low-tech-magazine-20122018/paperback/product-24028679.html">710-page perfect-bound paperback</a>&nbsp;which is printed on demand and contains 37 of the most recent articles from the website (2012 to 2018). A second volume, collecting articles published between 2007 and 2011, will appear later this year.</p>
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How (Not) to Run a Modern Society on Solar and Wind Power Alonetag:typepad.com,2003:post-6a00e0099229e8883301bb09bcb199970d2017-09-13T23:04:26+02:002017-09-13T23:04:26+02:00While the potential of wind and solar energy is more than sufficient to supply the electricity demand of industrial societies, these resources are only available intermittently. To ensure that supply always meets demand, a renewable power grid needs an oversized power generation and transmission capacity of up to ten times the peak demand. It also requires a balancing capacity of fossil fuel power plants, or its equivalent in energy storage. Consequently, matching supply to demand at all times makes renewable power production a complex, slow, expensive and unsustainable undertaking. Yet, if we would adjust energy demand to the variable supply of solar and wind energy, a renewable power grid could be much more advantageous. Using wind and solar energy only...kris de decker
<div xmlns="http://www.w3.org/1999/xhtml"><p><img class="asset asset-image at-xid-6a00e0099229e8883301b7c8f3edc1970b img-responsive" style="display: block; margin-left: auto; margin-right: auto;" title="Wind energy" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301b7c8f3edc1970b-500wi" alt="Wind energy" /></p>
<p>While the potential of wind and solar energy is more than sufficient to supply the electricity demand of industrial societies, these resources are only available intermittently. To ensure that supply always meets demand, a renewable power grid needs an oversized power generation and transmission capacity of up to ten times the peak demand. It also requires a balancing capacity of fossil fuel power plants, or its equivalent in energy storage.&nbsp;</p>
<p>Consequently, matching supply to demand at all times makes renewable power production a complex, slow, expensive and unsustainable undertaking.&nbsp;Yet, if we would adjust energy demand to the variable supply of solar and wind energy, a renewable power grid could be much more advantageous. Using wind and solar energy only when they're available is a traditional concept that modern technology can improve upon significantly.</p>
<p style="text-align: right;"><span style="background-color: #ffffbf;">Image: <a href="https://www.eyeofthewind.net/en/" target="_blank" rel="noopener noreferrer">Eye of the wind</a>.</span></p>
<h2 style="text-align: center;"><span style="font-size: 13pt; background-color: #ffffff;"><strong>100% Renewable Energy</strong></span></h2>
<p>It is widely believed that in the future, renewable energy production will allow modern societies to become independent from fossil fuels, with wind and solar energy having the largest potential. An oft-stated fact is that there's enough wind and solar power available to meet the energy needs of modern civilisation many times over.</p>
<p>For instance, in Europe, the practical wind energy potential for electricity production on- and off-shore is estimated to be at least 30,000 TWh per year, or ten times the annual electricity demand. [<span style="color: #c00000;">1</span>] In the USA, the technical solar power potential is estimated to be 400,000 TWh, or 100 times the annual electricity demand. [<span style="color: #c00000;">2</span>]</p>
<p>Such statements, although theoretically correct, are highly problematic in practice. This is because they are based on annual averages of renewable energy production, and do not address the highly variable and uncertain character of wind and solar energy.&nbsp;</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">Annual averages of renewable energy production do not address the highly variable and uncertain character of wind and solar energy</span></p>
</blockquote>
<p>Demand and supply of electricity need to be matched at all times, which is relatively easy to achieve with power plants that can be turned on and off at will. However, the&nbsp;output of wind turbines and solar panels is totally dependent on the whims of the weather.</p>
<p>Therefore, to find out if and how we can run a modern society on solar and wind power alone, we need to compare time-synchronised electricity demand with time-synchronised solar or wind power availability. [<span style="color: #c00000;">3</span>][<span style="color: #c00000;">4</span>] [<span style="color: #c00000;">5</span>] In doing so, it becomes clear that supply correlates poorly with demand.</p>
<hr />
<p><img class="asset asset-image at-xid-6a00e0099229e8883301b7c8f3f180970b img-responsive" title="The intermittency of solar en wind energy compared to demand" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301b7c8f3f180970b-500wi" alt="The intermittency of solar en wind energy compared to demand" style="display: block; margin-left: auto; margin-right: auto;" /></p>
<p style="text-align: center;"><span style="background-color: #ffffbf;">Above: a visualisation of 30 days of superimposed power demand time series data (red), wind energy generation data (blue), and solar insolation data (yellow). Average values are in colour-highlighted black lines. Data obtained from Bonneville Power Administration, April 2010. Source: [21]</span></p>
<hr />
<h2 style="text-align: center;"><span style="font-size: 13pt; background-color: #ffffff;"><strong>The Intermittency of Solar Energy</strong></span></h2>
<p style="text-align: left;">Solar power is characterised by both predictable and unpredictable variations. There is a predictable diurnal and seasonal pattern, where peak output occurs in the middle of the day and in the summer, depending on the apparent motion of the sun in the sky. [<span style="color: #c00000;">6</span>] [<span style="color: #c00000;">7</span>]</p>
<p style="text-align: left;">When the sun is lower in the sky, its rays have to travel through a larger air mass, which reduces their strength because they are absorbed by particles in the atmosphere. The sun's rays are also spread out over a larger horizontal surface, decreasing the energy transfer per unit of horizontal surface area.</p>
<p style="text-align: left;">When the sun is 60° above the horizon, the sun's intensity is still 87% of its maximum when it reaches a horizontal surface. However, at lower angles, the sun's intensity quickly decreases. At a solar angle of&nbsp;15°, the radiation that strikes a horizontal surface is only 25% of its maximum.&nbsp;</p>
<p>On a seasonal scale, the solar elevation angle also correlates with the number of daylight hours, which reduces the amount of solar energy received over the course of a day at times of the year when the sun is already lower in the sky. And, last but not least, there's no solar energy available at night.</p>
<p><a class="asset-img-link" style="display: inline;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301b7c91c390f970b-pi"><img class="asset asset-image at-xid-6a00e0099229e8883301b7c91c390f970b img-responsive" style="width: 700px;" alt="Cloud map" title="Cloud map" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301b7c91c390f970b-700wi" /></a></p>
<p style="text-align: center;"><span style="background-color: #ffffbf;">Image: Average cloud cover 2002 - 2015. Source: <a href="https://earthobservatory.nasa.gov/IOTD/view.php?id=85843&amp;eocn=image&amp;eoci=related_image" target="_blank" rel="noopener noreferrer" style="background-color: #ffffbf;">NASA</a>.</span></p>
<p>Likewise, the presence of clouds adds unpredictable variations to the solar energy supply. Clouds scatter and absorb solar radiation, reducing the amount of insolation that reaches the ground below. Solar output is roughly 80% of its maximum with a light cloud cover, but only 15% of its maximum on a heavy overcast day. [<span style="color: #c00000;">8</span>][<span style="color: #c00000;">9</span>][<span style="color: #c00000;">10</span>]</p>
<p>Due to a lack of thermal or mechanical inertia in solar photovoltaic (PV) systems, the changes due to clouds can be dramatic. For example, under fluctuating cloud cover, the output of multi-megawatt PV power plants in the Southwest USA was reported to have variations of roughly 50% in a 30 to 90 second timeframe and around 70% in a timeframe of 5 to 10 minutes. [<span style="color: #c00000;">6</span>]</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">In London, a solar panel produces 65 times less energy on a heavy overcast day in December at 10 am than on a sunny day in June at noon.&nbsp;</span></p>
</blockquote>
<p>The combination of these predictable and unpredictable variations in solar power makes it clear that the output of a solar power plant can vary enormously throughout time.&nbsp;In Phoenix, Arizona, the sunniest place in the USA, a solar panel produces on average 2.7 times less energy in December than in June. Comparing a sunny day at midday in June with a heavy overcast day at 10 am in December, the difference in solar output is almost twentyfold. [<span style="color: #00bf00;">11</span>]</p>
<p>In London, UK, which is a moderately suitable location for solar power, a solar panel produces on average 10 times less energy in December than in June. Comparing a sunny day in June at noon with a heavy overcast day in December at 10 am, the solar output differs by a factor of 65. [<span style="color: #c00000;">8</span>][<span style="color: #c00000;">9</span>]</p>
<h2 style="text-align: center;"><span style="font-size: 13pt; background-color: #ffffff;"><strong>The Intermittency of Wind Energy</strong></span></h2>
<p>Compared to solar energy, the variability of the wind is even more volatile. On the one hand, wind energy can be harvested both day and night, while on the other hand, it's less predictable and less reliable than solar energy. During daylight hours, there's always a minimum amount of solar power available, but this is not the case for wind, which can be absent or too weak for days or even weeks at a time. There can also be too much wind, and wind turbines then have to be shut down in order to avoid damage.</p>
<p>On average throughout the year, and depending on location, modern wind farms produce 10-45% of their rated maximum power capacity, roughly double the annual capacity factor of the average solar PV installation (5-30%). [<span style="color: #c00000;">6</span>] [<span style="color: #c00000;">12</span>][<span style="color: #c00000;">13</span>][<span style="color: #c00000;">14</span>] In practice, however, wind turbines can operate between 0 and 100% of their maximum power at any moment.</p>
<hr />
<p><img class="asset asset-image at-xid-6a00e0099229e8883301b8d2758646970c image-full img-responsive" title="Hourly wind power output on 29 different days in april 2005 at a wind plant in california" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301b8d2758646970c-800wi" alt="Hourly wind power output on 29 different days in april 2005 at a wind plant in california" border="0" /></p>
<p style="text-align: center;"><span style="background-color: #ffffbf;">Hourly wind power output on 29 different days in april 2005 at a wind plant in california. Source: [6]</span></p>
<hr />
<p>For many locations, only average wind speed data is available. However, the chart above shows the daily and hourly wind power output on 29 different days at a wind farm in California. At any given hour of the day and any given day of the month, wind power production can vary between zero and 600 megawatt, which is the maximum power production of the wind farm. [<span style="color: #c00000;">6</span>]</p>
<p>Even relatively small changes in wind speed have a large effect on wind power production: if the wind speed decreases by half, power production decreases by a factor of eight. [<span style="color: #c00000;">15</span>] Wind resources also vary throughout the years. Germany, the Netherlands and Denmark show a wind speed inter-annual variability of up to 30%. [<span style="color: #c00000;">1</span>] Yearly differences in solar power can also be significant. [<span style="color: #c00000;">16</span>] [<span style="color: #c00000;">17</span>]</p>
<h2 style="text-align: center;"><span style="font-size: 13pt; background-color: #ffffff;"><strong>How to Match Supply with Demand?</strong></span></h2>
<p>To some extent, wind and solar energy can compensate for each other. For example, wind is usually twice as strong during the winter months, when there is less sun. [<span style="color: #c00000;">18</span>] However, this concerns average values again. At any particular moment of the year, wind and solar energy may be weak or absent simultaneously, leaving us with little or no electricity at all.</p>
<p>Electricity demand also varies throughout the day and the seasons, but these changes are more predictable and much less extreme. Demand peaks in the morning and in the evening, and is at its lowest during the night. However, even at night, electricity use is still close to 60% of the maximum.&nbsp;</p>
<blockquote>
<p style="text-align: right; padding-left: 30px;"><span style="font-size: 13pt;">At any particular moment of the year, wind and solar energy may be weak or absent simultaneously, leaving us with little or no electricity at all.</span></p>
</blockquote>
<p>Consequently, if renewable power capacity is calculated based on the annual averages of solar and wind energy production and in tune with the average power demand, there would be huge electricity shortages for most of the time. To ensure that electricity supply always meets electricity demand, additional measures need to be taken.</p>
<p>First, we could count on a backup infrastructure of dispatchable fossil fuel power plants to supply electricity when there's not enough renewable energy available. Second, we could oversize the renewable generation capacity, adjusting it to the worst case scenario. Third, we could connect geographically dispersed renewable energy sources to smooth out variations in power production. Fourth, we could store surplus electricity for use in times when solar and/or wind resources are low or absent.</p>
<p><span style="background-color: #ffffff;">As we shall see, all of these strategies are self-defeating on a large enough scale, even when they're combined. </span><span style="background-color: #ffffff;">If the energy used for building and maintaining the extra infrastructure is accounted for in a life cycle analysis of a renewable power grid, it would be just as CO2-intensive as the present-day power grid.&nbsp;</span></p>
<h2 style="text-align: center;"><span style="font-size: 13pt; background-color: #ffffff;"><strong style="text-align: center;">Strategy 1: Backup Power Plants</strong></span></h2>
<p>Up to now, the relatively small share of renewable power sources added to the grid has been balanced by dispatchable forms of electricity, mainly rapidly deployable gas power plants. Although this approach completely "solves" the problem of intermittency, it results in a paradox because the whole point of switching to renewable energy is to become independent of fossil fuels, including gas. [<span style="color: #c00000;">19</span>]</p>
<p>Most scientific research focuses on Europe, which has the most ambitious plans for renewable power. For a power grid based on 100% solar and wind power, with no energy storage and assuming interconnection at the national European level only, the balancing capacity of fossil fuel power plants needs to be just as large as peak electricity demand. [<span style="color: #c00000;">12</span>] In other words, there would be just as many non-renewable power plants as there are today.</p>
<p><a class="asset-img-link" style="display: inline;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301b7c91c77f4970b-pi"><img class="asset asset-image at-xid-6a00e0099229e8883301b7c91c77f4970b image-full img-responsive" alt="Power plant capacity united states" title="Power plant capacity united states" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301b7c91c77f4970b-800wi" border="0" /></a></p>
<p style="text-align: center;"><span style="background-color: #ffffbf;">Every power plant in the USA. <a href="https://www.washingtonpost.com/graphics/national/power-plants/?utm_term=.5a41d6c60a94" target="_blank" rel="noopener noreferrer" style="background-color: #ffffbf;">Visualisation by The Washington Post</a>.</span></p>
<p>Such a hybrid infrastructure would lower the use of carbon fuels for the generation of electricity, because renewable energy can replace them if there is sufficient sun or wind available. However, lots of energy and materials need to be invested into what is essentially a double infrastructure. The energy that's saved on fuel is spent on the manufacturing, installation and interconnection of millions of solar panels and wind turbines.</p>
<p>Although the balancing of renewable power sources with fossil fuels is widely regarded as a temporary fix that's not suited for larger shares of renewable energy, most other technological strategies (described below) can only partially reduce the need for balancing capacity.</p>
<h2 style="text-align: center;"><span style="font-size: 13pt; background-color: #ffffff;"><strong>Strategy 2: Oversizing Renewable Power Production</strong></span></h2>
<p>Another way to avoid energy shortages is to install more solar panels and wind turbines. If solar power capacity is tailored to match demand during even the shortest and darkest winter days, and wind power capacity is matched to the lowest wind speeds, the risk of electricity shortages could be reduced significantly. However, the obvious disadvantage of this approach is an oversupply of renewable energy for most of the year.</p>
<p>During periods of oversupply, the energy produced by solar panels and wind turbines is curtailed in order to avoid grid overloading. Problematically, curtailment has a detrimental effect on the sustainability of a renewable power grid. It reduces the electricity that a solar panel or wind turbine produces over its lifetime, while the energy required to manufacture, install, connect and maintain it remains the same. Consequently, the capacity factor and the energy returned for the energy invested in wind turbines and solar panels decrease. [<span style="color: #00bf00;">20</span>]</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">Installing more solar panels and wind turbines reduces the risk of shortages, but it produces an oversupply of electricity for most of the year.</span></p>
</blockquote>
<p>Curtailment rates increase spectacularly as wind and solar comprise a larger fraction of the generation mix, because the overproduction's dependence on the share of renewables is exponential. Scientists calculated that a European grid comprised of 60% solar and wind power would require a generation capacity that's double the peak load, resulting in 300 TWh of excess electricity every year (roughly 10% of the current annual electricity consumption in Europe).</p>
<p>In the case of a grid with 80% renewables, the generation capacity needs to be six times larger than the peak load, while the excess electricity would be equal to 60% of the EU's current annual electricity consumption. Lastly, in a grid with 100% renewable power production, the generation capacity would need to be ten times larger than the peak load, and excess electricity would surpass the EU annual electricity consumption. [<span style="color: #c00000;">21</span>] [<span style="color: #c00000;">22</span>] [<span style="color: #c00000;">23</span>]&nbsp;</p>
<p>This means that up to ten times more solar panels and wind turbines need to be manufactured. The energy that's needed to create this infrastructure would make the switch to renewable energy self-defeating, because the energy payback times of solar panels and wind turbines would increase six- or ten-fold.</p>
<p>For solar panels, the energy payback would only occur in 12-24 years in a power grid with 80% renewables, and in 20-40 years in a power grid with 100% renewables. Because the life expectancy of a solar panel is roughly 30 years, a solar panel may never produce the energy that was needed to manufacture it. Wind turbines would remain net energy producers because they have shorter energy payback times, but their advantage compared to fossil fuels would decrease. [<span style="color: #00bf00;">24</span>]</p>
<h2 style="text-align: center;"><span style="font-size: 13pt; background-color: #ffffff;"><strong>Strategy 3: Supergrids</strong></span></h2>
<p>The variability of solar and wind power can also be reduced by interconnecting renewable power plants over a wider geographical region. For example, electricity can be overproduced where the wind is blowing but transmitted to meet demand in becalmed locations. [<span style="color: #c00000;">19</span>]</p>
<p>Interconnection also allows the combination of technologies that utilise different variable power resources, such as wave and tidal energy. [<span style="color: #c00000;">3</span>] Furthermore, connecting power grids over large geographical areas allows a wider sharing of backup fossil fuel power plants.</p>
<p><img class="asset asset-image at-xid-6a00e0099229e8883301b7c91c3715970b image-full img-responsive" alt="Wind map europe saturday september 2 2017 23h48" title="Wind map europe saturday september 2 2017 23h48" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301b7c91c3715970b-800wi" border="0" /></p>
<p style="text-align: center;"><span style="background-color: #ffffbf;">Wind map of Europe, September 2, 2017, 23h48. Source:&nbsp;<a href="https://www.windy.com/" rel="noopener noreferrer" target="_blank" style="background-color: #ffffbf;">Windy</a>.</span></p>
<p>Although today's power systems in Europe and the USA stretch out over a large enough area, these grids are currently not strong enough to allow interconnection of renewable energy sources. This can be solved with a powerful overlay high-voltage DC transmission grid. Such "supergrids" form the core of many ambitious plans for 100% renewable power production, especially in Europe. [<span style="color: #c00000;">25</span>] The problem with this strategy is that transmission capacity needs to be overbuilt, over very long distances. [<span style="color: #c00000;">19</span>]</p>
<p>For a European grid with a share of 60% renewable power (an optimal mix of wind and solar), grid capacity would need to be increased at least sevenfold. If individual European countries would disregard national concerns about security of supply, and backup balancing capacity would be optimally distributed throughout the continent, the necessary grid capacity extensions can be limited to about triple the existing European high-voltage grid. For a European power grid with a share of 100% renewables, grid capacity would need to be up to twelve times larger than it is today. [<span style="color: #c00000;">21</span>] [<span style="color: #c00000;">26</span>][<span style="color: #00bf00;">27</span>]</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">Even in the UK, which has one of the best renewable energy sources in the world, combining wind, sun, wave and tidal power would still generate electricity shortages for 65 days per year.</span></p>
</blockquote>
<p>The problems with such grid extensions are threefold. Firstly, building infrastructure such as transmission towers and their foundations, power lines, substations, and so on, requires a significant amount of energy and other resources. This will need to be taken into account when making a life cycle analysis of a renewable power grid. As with oversizing renewable power generation, most of the oversized transmission infrastructure will not be used for most of the time, driving down the transmission capacity factor substantially.</p>
<p>Secondly, a supergrid involves transmission losses, which means that more wind turbines and solar panels will need to be installed to compensate for this loss. Thirdly, the acceptance of and building process for new transmission lines can take up to ten years. [<span style="color: #c00000;">20</span>][<span style="color: #c00000;">25</span>] This is not just bureaucratic hassle: transmission lines have a high impact on the land and often face local opposition, which makes them one of the main obstacles for the growth of renewable power production.</p>
<p>Even with a supergrid, low power days remain a possibility over areas as large as Europe. With a share of 100% renewable energy sources and 12 times the current grid capacity, the balancing capacity of fossil fuel power plants can be reduced to 15% of the total annual electricity consumption, which represents the maximum possible benefit of transmission for Europe. [<span style="color: #c00000;">28</span>]</p>
<p>Even in the UK, which has one of the best renewable energy sources in the world, interconnecting wind, sun, wave and tidal power would still generate electricity shortages for 18% of the time (roughly 65 days per year). [<span style="color: #c00000;">29</span>] [<span style="color: #00bf00;">30</span>][<span style="color: #00bf00;">31</span>]</p>
<h2 style="text-align: center;"><span style="font-size: 13pt; background-color: #ffffff;"><strong>Strategy 4: Energy Storage</strong></span></h2>
<p>A final strategy to match supply to demand is to store an oversupply of electricity for use when there is not enough renewable energy available. Energy storage avoids curtailment and it's the only supply-side strategy that can make a balancing capacity of fossil fuel plants redundant, at least in theory. In practice, the storage of renewable energy runs into several problems.</p>
<p>First of all, while there's no need to build and maintain a backup infrastructure of fossil fuel power plants, this advantage is negated by the need to build and maintain an energy storage infrastructure. Second, all storage technologies have charging and discharging losses, which results in the need for extra solar panels and wind turbines to compensate for this loss.&nbsp;</p>
<p><a class="asset-img-link" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301bb09bfeaa9970d-pi"><img class="asset asset-image at-xid-6a00e0099229e8883301bb09bfeaa9970d img-responsive" alt="Wind map usa" title="Wind map usa" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301bb09bfeaa9970d-700wi" /></a></p>
<p style="text-align: center;"><a href="http://hint.fm/wind/" target="_blank" rel="noopener noreferrer">Live wind map of the USA</a>.&nbsp;</p>
<p>The energy required to build and maintain the storage infrastructure and the extra renewable power plants need to be taken into account when conducting a life cycle analysis of a renewable power grid. In fact, research has shown that it can be more energy efficient to curtail renewable power from wind turbines than to store it, because the energy needed to manufacture storage and operate it (which involves charge-discharge losses) surpasses the energy that is lost through curtailment. [<span style="color: #c00000;">23</span>]</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">If we count on electric cars to store the surplus of renewable electricity, their batteries would need to be 60 times larger than they are today</span></p>
</blockquote>
<p>It has been calculated that for a European power grid with 100% renewable power plants (670 GW wind power capacity and 810 GW solar power capacity) and no balancing capacity, the energy storage capacity needs to be 1.5 times the average monthly load and amounts to 400 TWh, not including charging and discharging losses. [<span style="color: #c00000;">32</span>] [<span style="color: #c00000;">33</span>] [<span style="color: #c00000;">34</span>]</p>
<p>To give an idea of what this means: the most optimistic estimation of Europe's total potential for pumped hydro-power energy storage is 80 TWh [<span style="color: #c00000;">35</span>], while converting all 250 million passenger cars in Europe to electric drives with a 30 kWh battery would result in a total energy storage of 7.5 TWh. In other words, if we count on electric cars to store the surplus of renewable electricity, their batteries would need to be 60 times larger than they are today (and that's without allowing for the fact that electric cars will substantially increase power consumption).</p>
<p>Taking into account a charging/discharging efficiency of 85%, manufacturing 460 TWh of lithium-ion batteries would require 644 million Terajoule of primary energy, which is equal to 15 times the annual primary energy use in Europe. [<span style="color: #c00000;">36</span>] This energy investment would be required at minimum every twenty years, which is the most optimistic life expectancy of lithium-ion batteries. There are many other technologies for storing excess electricity from renewable power plants, but all have unique disadvantages that make them unattractive on a large scale. [<span style="color: #c00000;">37</span>] [<span style="color: #c00000;">38</span>]</p>
<h2 style="text-align: center;"><span style="font-size: 13pt; background-color: #ffffff;"><strong>Matching Supply to Demand = Overbuilding the Infrastructure</strong></span></h2>
<p>In conclusion, calculating only the energy payback times of individual solar panels or wind turbines greatly overestimates the sustainability of a renewable power grid. If we want to match supply to demand at all times, we also need to factor in the energy use for overbuilding the power generation and transmission capacity, and the energy use for building the backup generation capacity and/or the energy storage. The need to overbuild the system also increases the costs and the time required to switch to renewable energy.</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">Calculating only the energy payback times of individual solar panels or wind turbines greatly overestimates the sustainability of a renewable power grid.</span></p>
</blockquote>
<p>Combining different strategies is a more synergistic approach which improves the sustainability of a renewable power grid, but these advantages are not large enough to provide a fundamental solution. [<span style="color: #c00000;">33</span>] [<span style="color: #c00000;">39</span>] [<span style="color: #c00000;">40</span>]</p>
<p>Building solar panels, wind turbines, transmission lines, balancing capacity and energy storage using renewable energy instead of fossil fuels doesn't solve the problem either, because it also assumes an overbuilding of the infrastructure:&nbsp;we would need to build an extra renewable energy infrastructure to build the renewable energy infrastructure.</p>
<h2 style="text-align: center;"><span style="font-size: 13pt; background-color: #ffffff;"><strong>Adjusting Demand to Supply</strong></span></h2>
<p style="text-align: left;">However, this doesn't mean that a sustainable renewable power grid is impossible. There's a fifth strategy, which does not try to match supply to demand, but instead aims to match demand to supply. In this scenario, renewable energy would ideally be used only when it's available.&nbsp;</p>
<p style="text-align: left;">If we could manage to adjust all energy demand to variable solar and wind resources, there would be no need for grid extensions, balancing capacity or overbuilding renewable power plants. Likewise, all the energy produced by solar panels and wind turbines would be utilised, with no transmission losses and no need for curtailment or energy storage. &nbsp;</p>
<p><a class="asset-img-link" style="display: inline;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301b7c91eaf6f970b-pi"><img class="asset asset-image at-xid-6a00e0099229e8883301b7c91eaf6f970b image-full img-responsive" alt="Moulbaix Belgium the windmill de la Marquise XVII XVIIIth centuries" title="Moulbaix Belgium the windmill de la Marquise XVII XVIIIth centuries" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301b7c91eaf6f970b-800wi" border="0" /></a></p>
<p style="text-align: center;"><span style="background-color: #ffffbf;">Windmill in Moulbaix, Belgium, 17th/18th century. Image: <a href="https://commons.wikimedia.org/wiki/File:Moulbaix_MV1aJPG.jpg" target="_blank" rel="noopener noreferrer">Jean-Pol GrandMont</a>.</span></p>
<p style="text-align: left;">Of course, adjusting energy demand to energy supply at all times is impossible, because not all energy using activities can be postponed. However, the adjustment of energy demand to supply should take priority, while the other strategies should play a supportive role. If&nbsp;we let go of the need to match energy demand for 24 hours a day and 365 days a year, a renewable power grid could be built much faster and at a lower cost, making it more sustainable overall.</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">If we could manage to adjust all energy demand to variable solar and wind resources, there would no need for energy storage, grid extensions, balancing capacity or overbuilding renewable power plants.</span></p>
</blockquote>
<p>With regards to this adjustment, even small compromises yield very beneficial results. For example, if the UK would accept electricity shortages for 65 days a year, it could be powered by a 100% renewable power grid (solar, wind, wave &amp; tidal power) without the need for energy storage, a backup capacity of fossil fuel power plants, or a large overcapacity of power generators. [<span style="color: #c00000;">29</span>]&nbsp;</p>
<p>If demand management is discussed at all these days, it's usually limited to so-called 'smart' household devices, like washing machines or dishwashers that automatically turn on when renewable energy supply is plentiful. However, these ideas are only scratching the surface of what's possible.</p>
<p>Before the Industrial Revolution, both industry and transportation were largely dependent on intermittent renewable energy sources. The variability in the supply was almost entirely solved by adjusting energy demand. For example, windmills and sailing boats only operated when the wind was blowing. <a href="http://www.lowtechmagazine.com/2017/09/how-to-run-the-economy-on-the-weather.html">In the next article, I will explain how this historical approach could be successfully applied to modern industry and cargo transportation</a>.</p>
<p>Kris De Decker (edited by Jenna Collett)</p>
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<p><span style="font-size: 12pt; background-color: #ffffff;"><strong>Sources:</strong></span><strong><span style="text-decoration: underline;"><br /></span></strong></p>
<p>[1] Swart, R. J., et al. <a href="http://library.wur.nl/WebQuery/wurpubs/reports/387099" target="_blank" rel="noopener noreferrer"><em>Europe's onshore and offshore wind energy potential, an assessment of environmental and economic constraints</em></a>. No. 6/2009. European Environment Agency, 2009.</p>
<p>[2] Lopez, Anthony, et al. <a href="http://dspace.bhos.edu.az/jspui/bitstream/123456789/1093/1/us_%20renewable%20energy%20potential.pdf" target="_blank" rel="noopener noreferrer"><em>US renewable energy technical potentials: a GIS-based analysis</em></a>. NREL, 2012. See also&nbsp;<a href="http://www.businessinsider.com/map-shows-solar-panels-to-power-the-earth-2015-9" target="_blank" rel="noopener noreferrer">Here's how much of the world would need to be covered in solar panels to power Earth</a>, Business Insider, October 2015.</p>
<p>[3] Hart, Elaine K., Eric D. Stoutenburg, and Mark Z. Jacobson. "<a href="https://www.researchgate.net/profile/Mark_Jacobson2/publication/220473405_The_Potential_of_Intermittent_Renewables_to_Meet_Electric_Power_Demand_Current_Methods_and_Emerging_Analytical_Techniques/links/0046351dae36f1fd77000000.pdf" target="_blank" rel="noopener noreferrer">The potential of intermittent renewables to meet electric power demand: current methods and emerging analytical techniques</a>." <em>Proceedings of the IEEE</em> 100.2 (2012): 322-334.</p>
<p>[4] Ambec, Stefan, and Claude Crampes. <a href="http://core.ac.uk/download/pdf/6567478.pdf" target="_blank" rel="noopener noreferrer"><em>Electricity production with intermittent sources of energy</em></a>. No. 10.07. 313. LERNA, University of Toulouse, 2010.<a href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.177.7361&amp;rep=rep1&amp;type=pdf"></a></p>
<p>[5] Mulder, F. M. "<a href="http://aip.scitation.org/doi/full/10.1063/1.4874845" target="_blank" rel="noopener noreferrer">Implications of diurnal and seasonal variations in renewable energy generation for large scale energy storage</a>." <em>Journal of Renewable and Sustainable Energy</em> 6.3 (2014): 033105.</p>
<p>[6] INITIATIVE, MIT ENERGY. "<a href="https://energy.mit.edu/wp-content/uploads/2012/03/MITEI-RP-2011-001.pdf" target="_blank" rel="noopener noreferrer">Managing large-scale penetration of intermittent renewables</a>." (2012).</p>
<p>[7] Richard Perez, Mathieu David, Thomas E. Hoff, Mohammad Jamaly, Sergey Kivalov, Jan Kleissl, Philippe Lauret and Marc Perez (2016), "<a href="http://www.nowpublishers.com/article/Details/REN-006" target="_blank" rel="noopener noreferrer">Spatial and temporal variability of solar energy</a>", Foundations and Trends in Renewable Energy: Vol. 1: No. 1, pp 1-44. http://dx.doi.org/10.1561/2700000006</p>
<p>[8] <a href="http://www.ftexploring.com/solar-energy/sun-angle-and-insolation2.htm" target="_blank" rel="noopener noreferrer">Sun Angle and Insolation</a>. FTExploring.</p>
<p>[9] &nbsp;<a href="https://www.sunearthtools.com/dp/tools/pos_sun.php?lang=en" target="_blank" rel="noopener noreferrer">Sun position calculator</a>, Sun Earth Tools.</p>
<p>[10] Burgess, Paul. " <a href="http://ccfg.org.uk/conferences/downloads/P_Burgess.pdf" target="_blank" rel="noopener noreferrer">Variation in light intensity at different latitudes and seasons effects of cloud cover</a>, and the amounts of direct and diffused light." <em>Forres, UK: Continuous Cover Forestry Group. Available online at http://www. ccfg. org. uk/conferences/downloads/P_Burgess. pdf</em>. 2009.</p>
<p>[11]&nbsp;Solar output can be increased, especially in winter, by tilting solar panels so that they make a 90 degree angle with the sun's rays. However, this only addresses the spreading out of solar irradiation and has no effect on the energy lost because of the greater air mass, nor on the amount of daylight hours. Furthermore, tilting the panels is always a compromise. A panel that's ideally tilted for the winter sun will be less efficient in the summer sun, and the other way around.</p>
<p>[12] Schaber, Katrin, Florian Steinke, and Thomas Hamacher. "<a href="http://pubman.mpdl.mpg.de/pubman/item/escidoc:2145949/component/escidoc:2145948/Schaber_Transmission.pdf" target="_blank" rel="noopener noreferrer">Transmission grid extensions for the integration of variable renewable energies in europe: who benefits where</a>?." <em>Energy Policy</em> 43 (2012): 123-135.</p>
<p>[13]&nbsp;<a href="http://energynumbers.info/germanys-offshore-wind-capacity-factors" target="_blank" rel="noopener noreferrer">German offshore wind capacity factors</a>, Energy Numbers, July 2017</p>
<p>[14] <a href="https://carboncounter.wordpress.com/2015/07/24/what-are-the-capacity-factors-of-americas-wind-farms/" target="_blank" rel="noopener noreferrer">What are the capacity factors of America's wind farms</a>? Carbon Counter, 24 July 2015.</p>
<p>[15] Sorensen, Bent. <a href="https://www.cabdirect.org/cabdirect/abstract/20113242749" target="_blank" rel="noopener noreferrer"><em>Renewable Energy: physics, engineering, environmental impacts, economics &amp; planning</em></a>; Fourth Edition. Elsevier Ltd, 2010.</p>
<p>[16] Jerez, S., et al. "<a href="http://journals.ametsoc.org/doi/full/10.1175/JAMC-D-12-0257.1" target="_blank" rel="noopener noreferrer">The Impact of the North Atlantic Oscillation on Renewable Energy Resources in Southwestern Europe</a>." <em>Journal of applied meteorology and climatology</em> 52.10 (2013): 2204-2225.</p>
<p>[17] Eerme, Kalju. "<a href="https://cdn.intechopen.com/pdfs-wm/33343.pdf" target="_blank" rel="noopener noreferrer">Interannual and intraseasonal variations of the available solar radiation</a>." <em>Solar Radiation</em>. InTech, 2012.</p>
<p>[18] Archer, Cristina L., and Mark Z. Jacobson. "<a href="http://www.ceoe.udel.edu/File%20Library/Our%20People/Profiles/carcher/My_Papers/Archer_Jacobson_Applied_Geography_practical_wind_2013.pdf" target="_blank" rel="noopener noreferrer">Geographical and seasonal variability of the global practical wind resources</a>." <em>Applied Geography</em> 45 (2013): 119-130.</p>
<p>[19] Rugolo, Jason, and Michael J. Aziz. "<a href="https://aziz.seas.harvard.edu/files/mja212.pdf" target="_blank" rel="noopener noreferrer">Electricity storage for intermittent renewable sources</a>." <em>Energy &amp; Environmental Science</em> 5.5 (2012): 7151-7160.</p>
<p><span style="background-color: #ffffff;">[20] Even at today's relatively low shares of renewables, curtailment is already happening, caused by either transmission congestion, insufficient transmission availability, or minimal operating levels on thermal generators (coal and atomic power plants are designed to operate continuously). See: “<a href="http://www.academia.edu/download/45365857/Wind_and_Solar_Curtailment20160504-10660-14etuci.pdf" target="_blank" rel="noopener noreferrer">Wind and solar curtailment</a>”, Debra Lew et al., National Renewable Energy Laboratory, 2013. </span><span style="background-color: #ffffff;">For example, in China, now the world's top wind power producer, nearly one-fifth of total wind power is curtailed. See: <a href="http://uk.reuters.com/article/uk-china-windpower/chinese-wind-earnings-under-pressure-with-fifth-of-farms-idle-idUKKBN0O20VW20150517" target="_blank" rel="noopener noreferrer">Chinese wind earnings under pressure with fifth of farms idle</a>, Sue-Lin Wong &amp; Charlie Zhu, Reuters, May 17, 2015. </span></p>
<p>[21] Barnhart, Charles J., et al. "<a href="http://pubs.rsc.org/-/content/articlehtml/2013/ee/c3ee41973h" target="_blank" rel="noopener noreferrer">The energetic implications of curtailing versus storing solar- and wind-generated electricity</a>." <em>Energy &amp; Environmental Science</em> 6.10 (2013): 2804-2810.</p>
<p>[22] Schaber, Katrin, et al. "<a href="http://pubman.mpdl.mpg.de/pubman/item/escidoc:2145834/component/escidoc:2145833/Schaber_Parametric.pdf" target="_blank" rel="noopener noreferrer">Parametric study of variable renewable energy integration in europe: advantages and costs of transmission grid extensions</a>." <em>Energy Policy</em> 42 (2012): 498-508.</p>
<p>[23] Schaber, Katrin, Florian Steinke, and Thomas Hamacher. "<a href="http://www.internationalenergyworkshop.org/docs/IEW%202013_4E3paperSchaber.pdf" target="_blank" rel="noopener noreferrer">Managing temporary oversupply from renewables efficiently: electricity storage versus energy sector coupling in Germany</a>." <em>International Energy Workshop, Paris</em>. 2013.</p>
<p>[24] Underground cables can partly overcome this problem, but they are about 6 times more expensive than overhead lines.</p>
<p>[25] Szarka, Joseph, et al., eds. <a href="https://books.google.es/books?hl=nl&amp;lr=&amp;id=EEq-_ENyC-0C&amp;oi=fnd&amp;pg=PP2&amp;dq=Learning+from+wind+power:+governance,+societal+and+policy+perspectives+on+sustainable+energy&amp;ots=ptDfwLXaYb&amp;sig=Al3USP_vbrg4c7d4oyr_Cj4fzi8&amp;redir_esc=y#v=onepage&amp;q=Learning%20from%20wind%20power%3A%20governance%2C%20societal%20and%20policy%20perspectives%20on%20sustainable%20energy&amp;f=false" target="_blank" rel="noopener noreferrer"><em>Learning from wind power: governance, societal and policy perspectives on sustainable energy</em></a>. Palgrave Macmillan, 2012.</p>
<p>[26] Rodriguez, Rolando A., et al. "<a href="https://arxiv.org/pdf/1306.1079.pdf" target="_blank" rel="noopener noreferrer">Transmission needs across a fully renewable european storage system</a>." <em>Renewable Energy</em> 63 (2014): 467-476.</p>
<p>[27] Furthermore, new transmission capacity is often required to connect renewable power plants to the rest of the grid in the first place -- solar and wind farms must be co-located with the resource itself, and often these locations are far from the place where the power will be used.</p>
<p>[28] Becker, Sarah, et al. "<a href="https://arxiv.org/pdf/1307.1723.pdf" target="_blank" rel="noopener noreferrer">Transmission grid extensions during the build-up of a fully renewable pan-European electricity supply</a>." <em>Energy</em> 64 (2014): 404-418.</p>
<p>[29] <a href="http://zerocarbonbritain.com/images/pdfs/ZCBrtflo-res.pdf" target="_blank" rel="noopener noreferrer">Zero Carbon britain: Rethinking the Future</a>, Paul Allen et al., Centre for Alternative Technology, 2013</p>
<p>[30] Wave energy often correlates with wind power: if there's no wind, there's usually no waves.</p>
<p>[31] Building even larger supergrids to take advantage of even wider geographical regions, or even the whole planet, could make the need for balancing capacity largely redundant. However, this could only be done at very high costs and increased transmission losses. The transmission costs increase faster than linear with distance traveled since also the amount of peak power to be transported will grow with the surface area that is connected. [5] Practical obstacles also abound. For example, supergrids assume peace and good understanding between and within countries, as well as equal interests, while in reality some benefit much more from interconnection than others. [22]</p>
<p>[32] Heide, Dominik, et al. "<a href="https://www.researchgate.net/profile/Martin_Greiner2/publication/44853965_Seasonal_optimal_mix_of_wind_and_solar_power_in_a_future_highly_renewable_Europe/links/02e7e52a17a215ad6e000000/Seasonal-optimal-mix-of-wind-and-solar-power-in-a-future-highly-renewable-Europe.pdf" target="_blank" rel="noopener noreferrer">Seasonal optimal mix of wind and solar power in a future, highly renewable Europe</a>." <em>Renewable Energy</em> 35.11 (2010): 2483-2489.</p>
<p>[33] Rasmussen, Morten Grud, Gorm Bruun Andresen, and Martin Greiner. "<a href="https://mediatum.ub.tum.de/doc/1120528/1120528.pdf" target="_blank" rel="noopener noreferrer">Storage and balancing synergies in a fully or highly renewable pan-european system</a>." <em>Energy Policy</em> 51 (2012): 642-651.</p>
<p>[34] Weitemeyer, Stefan, et al. "<a href="https://arxiv.org/pdf/1405.2857" target="_blank" rel="noopener noreferrer">Integration of renewable energy sources in future power systems: the role of storage</a>." <em>Renewable Energy</em> 75 (2015): 14-20.</p>
<p>[35] <a href="https://ec.europa.eu/jrc/sites/jrcsh/files/jrc_20130503_assessment_european_phs_potential.pdf" target="_blank" rel="noopener noreferrer">Assessment of the European potential for pumped hydropower energy storage</a>, Marcos Gimeno-Gutiérrez et al., European Commission, 2013&nbsp;</p>
<p>[36] The calculation is based on the data in this article: <a href="http://www.lowtechmagazine.com/2015/05/sustainability-off-grid-solar-power.html" target="_blank" rel="noopener noreferrer">How sustainable is stored sunlight?</a> Kris De Decker, Low-tech Magazine, 2015.</p>
<p>[37] Evans, Annette, Vladimir Strezov, and Tim J. Evans. "<a href="http://www.academia.edu/download/32218343/energy_storage_systems_overview_2012.PDF" target="_blank" rel="noopener noreferrer">Assessment of utility energy storage options for increased renewable energy penetration</a>." <em>Renewable and Sustainable Energy Reviews</em> 16.6 (2012): 4141-4147.</p>
<p>[38] Zakeri, Behnam, and Sanna Syri. <a href="https://www.researchgate.net/profile/Behnam_Zakeri/publication/281277805_Electrical_energy_storage_systems_A_comparative_life_cycle_cost_analysis_2015/links/55deac0008ae79830bb58ede.pdf" target="_blank" rel="noopener noreferrer">"Electrical energy storage systems: A comparative life cycle cost analysis</a>." <em>Renewable and Sustainable Energy Reviews</em> 42 (2015): 569-596.</p>
<p>[39] Steinke, Florian, Philipp Wolfrum, and Clemens Hoffmann. "<a href="http://www.sciencedirect.com/science/article/pii/S0960148112004818" target="_blank" rel="noopener noreferrer">Grid vs. storage in a 100% renewable Europe</a>." <em>Renewable Energy</em> 50 (2013): 826-832.</p>
<p>[40] Heide, Dominik, et al. "<a href="http://www.sciencedirect.com/science/article/pii/S0960148111000851" target="_blank" rel="noopener noreferrer">Reduced storage and balancing needs in a fully renewable European power system with excess wind and solar power generation</a>." <em>Renewable Energy</em> 36.9 (2011): 2515-2523.<span style="background-color: #ffffff;"><br /></span></p>
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The bright future of solar thermal powered factoriestag:typepad.com,2003:post-6a00e0099229e88833015433fc3198970c2011-07-26T02:26:24+02:002014-06-01T12:50:21+02:00Most of the talk about renewable energy is aimed at electricity production. However, most of the energy we need is heat, which solar panels and wind turbines cannot produce efficiently. To power industrial processes like the making of chemicals, the smelting of metals or the production of microchips, we need a renewable source of thermal energy. Direct use of solar energy can be the solution, and it creates the possibility to produce renewable energy plants using only renewable energy plants, paving the way for a truly sustainable industrial civilization. Picture: ARUN. ---------------------------------------------------------------------------------------------------------------------------------------------- The missing element in our sustainable energy strategy is a renewable source of heat energy ---------------------------------------------------------------------------------------------------------------------------------------------- A large share of energy consumed worldwide is by heat. Cooking, space...kris de decker
<div xmlns="http://www.w3.org/1999/xhtml"><p style="text-align: left;"><a class="asset-img-link" style="display: inline;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301a3fd14b795970b-pi"><img class="asset asset-image at-xid-6a00e0099229e8883301a3fd14b795970b image-full img-responsive" title="Arun solar concentrator india" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301a3fd14b795970b-800wi" alt="Arun solar concentrator india" border="0" /></a></p>
<p style="text-align: left;">Most of the talk about renewable energy is aimed at electricity production. However, most of the energy we need is heat, which solar panels and wind turbines cannot produce efficiently. To power industrial processes like the making of chemicals, the smelting of metals or the production of microchips, we need a renewable source of thermal energy. Direct use of solar energy can be the solution, and it creates the possibility to produce renewable energy plants using only renewable energy plants, paving the way for a truly sustainable industrial civilization.</p>
<p style="text-align: right;"> <span style="font-size: 8pt;">Picture: <a href="http://www.clique.in/arun.html" target="_blank">ARUN</a>.</span></p>
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<p style="text-align: right; padding-left: 210px;"><span style="font-size: 13pt;">The missing element in our sustainable energy strategy is a renewable source of heat energy</span></p>
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<p>A large share of energy consumed worldwide is by heat. Cooking, space heating and water heating dominate domestic energy consumption. In the UK, these activities account for <a href="http://www.decc.gov.uk/en/content/cms/statistics/publications/dukes/dukes.aspx" target="_blank">85 percent</a> of domestic energy use, in Europe for <a href="http://www.odyssee-indicators.org/reports/household/households.pdf" target="_blank">89 percent</a> and in the USA for <a href="http://www.eia.gov/consumption/residential/reports/electronics.cfm" target="_blank">61 percent</a> (excluding cooking).</p>
<p>Heat also dominates industrial energy consumption. In the UK, <a href="http://webarchive.nationalarchives.gov.uk/+/http://www.berr.gov.uk/files/file11250.pdf" target="_blank">76 percent</a> of industrial energy consumption is heat. In Europe, this is <a href="http://www.estif.org/fileadmin/estif/content/policies/downloads/D23-solar-industrial-process-heat.pdf" target="_blank">67 percent</a>. I could not find figures for the US and for the world as a whole, but these percentages must be similar (and probably even higher on a worldwide scale because many energy-intensive industries have been outsourced to developing countries). Few things can be manufactured without heat.</p>
<p><span style="font-size: 13pt;">Solar panels and wind turbines are no producers of heat energy</span></p>
<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833015433c77e19970c-pi"><img class="asset asset-image at-xid-6a00e0099229e88833015433c77e19970c" style="margin: 0px 0px 5px 5px;" title="Blast furnace wikipedia" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833015433c77e19970c-320wi" alt="Blast furnace wikipedia" /></a> The importance of heat in total energy consumption sharply contrasts with our efforts to green the energy infrastructure. These are largely aimed at renewable electricity production using wind turbines and solar panels. Although it is perfectly possible to convert electricity into heat, as in electric heaters or electric cookers, it is very inefficient to do so.</p>
<p>It is often assumed that our energy problems are solved when renewables reach 'grid parity' - the point at which they can generate electricity for the same price as fossil fuels. But to truly compete with fossil fuels, renewables must also reach '<a href="http://www.solarfire.org/The-Thermal-Problem" target="_blank">thermal parity</a>'.</p>
<p>Though today in some locations it may be as cheap to produce electricity with wind or solar energy as with gas or coal, it still remains significantly cheaper to produce heat with oil, gas or coal than with a wind turbine or a solar panel. This is because it takes 2 to 3 kWh of fossil fuel thermal energy to create 1 kWh of electricity, so it is at least 2 to 3 times cheaper to make heat by simply burning the fossil fuels directly than to use an electric renewable technology at grid parity.</p>
<p><span style="font-size: 13pt;">Manufacturing wind turbines and solar panels requires heat</span></p>
<p>This means that solar panels and wind turbines will have to become two to three times cheaper than they are today in order to reach thermal parity with fossil fuels. This might sound reasonably possible, especially if you expect fossil fuel prices to rise. But consider this: even though they are intended to replace fossil fuels, renewable energy sources like wind turbines and solar panels are in fact dependent on a continuous supply of fossil fuels.&nbsp;</p>
<p>Solar panels and wind turbines do not need fossil fuels to operate, but they do <a href="http://www.lowtechmagazine.com/2008/03/the-ugly-side-o.html" target="_blank">need fossil fuels for their production</a>. You won't find any factory manufacturing PV solar panels or wind turbines using energy from their own PV solar panels or wind turbines. Why not? Because it would be 2 to 3 times more expensive to generate heat with solar panels or wind turbines than with fossil fuels. Yet to make solar panels and wind turbines, to produce steel and silicon for instance, heat is what is most needed. This means that the production costs of solar panels and wind turbines will be affected negatively by rising fossil fuel prices.</p>
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<p style="text-align: right; padding-left: 120px;"><span style="font-size: 13pt;">You won't find any factory manufacturing PV solar panels using energy from their own PV solar panels, because it would be 2 to 3 times more expensive to generate the heat required for producing steel and silicon<br /></span></p>
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<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301538ff5ba6c970b-pi"><br /></a> <a style="float: left;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833014e89f1db13970d-pi"><img class="asset asset-image at-xid-6a00e0099229e88833014e89f1db13970d" style="margin: 0px 5px 5px 0px;" title="Arun 2" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833014e89f1db13970d-800wi" alt="Arun 2" border="0" /></a> The same goes for batteries, which are an essential element of <a href="http://www.lowtechmagazine.com/electric-cars/" target="_blank">electric cars</a> and renewable electricity storage, and for many other modern green technologies, like LEDs and heat pumps. They require heat for their production, and this heat can be delivered at least 2 to 3 times cheaper by burning fossil fuels than by using wind turbines or solar panels (cheap electricity from hydropower plants is also an option, but has limited potential). This is a fundamental problem, because we will have to produce new wind turbines and solar panels every 20 to 30 years, and new batteries every 5 to 10 years.</p>
<p><span style="font-size: 13pt;">Renewable source of heat energy</span></p>
<p>The missing element in our sustainable energy strategy is a renewable source of thermal energy. Geothermal energy produces heat, but its potential is limited to regions that have volcanoes. Biomass is another option, but it faces <a href="http://www.lowtechmagazine.com/2008/04/algae-fuel-biof.html" target="_blank">many problems</a>. If we were to try to provide an important share of heat demand by burning biomass, we would quickly come up against the limits of what the planet can produce. There is only one source of heat energy left, and it is a powerful and inexhaustible one: solar energy.</p>
<p>We tend to see solar energy as yet another way to generate electricity, using photovoltaic panels or solar thermal power plants. But solar energy can also be applied directly, without the intermediate step of generating electricity. Basically, harvesting direct solar energy can happen in two ways: by means of water-based <a href="http://en.wikipedia.org/wiki/Solar_thermal_collector#Flat_plate_collectors" target="_blank">flat plate collectors</a> or <a href="http://en.wikipedia.org/wiki/Solar_thermal_collector#Evacuated_tube_collectors" target="_blank">evacuated tube collectors</a>, which collect solar radiation from all directions and can reach temperatures of 120 °C (248 °F), and by means of <a href="http://en.wikipedia.org/wiki/Concentrated_solar_power" target="_blank">solar concentrator collectors</a>, which track the sun, concentrate its radiation, and can generate much higher temperatures. These can be <a href="http://en.wikipedia.org/wiki/Parabolic_trough" target="_blank">parabolic trough systems</a>, <a href="http://en.wikipedia.org/wiki/Compact_Linear_Fresnel_Reflector" target="_blank">linear concentrating Fresnel collectors</a>, <a href="http://en.wikipedia.org/wiki/Solar_thermal#Dish_designs" target="_blank">parabolic dish systems</a> or <a href="http://www.google.com/url?sa=t&amp;source=web&amp;cd=1&amp;ved=0CCAQFjAA&amp;url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSolar_power_tower&amp;rct=j&amp;q=solar%20power%20towers&amp;ei=i5QkTsuFLouj-gb0xIm2Aw&amp;usg=AFQjCNGFb24urlsAiW1aZPaeC0skNlMi-A&amp;sig2=6AprD8HN-mfNI5aNwKLlPw&amp;cad=rja" target="_blank">solar power towers</a>. Almost all of these technologies were developed at the turn of the 20th century.</p>
<p><span style="font-size: 13pt;">Solar thermal power versus solar thermal heat</span></p>
<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833015433c835cd970c-pi"><img class="asset asset-image at-xid-6a00e0099229e88833015433c835cd970c" style="margin: 0px 0px 5px 5px;" title="Solar power tower" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833015433c835cd970c-320wi" alt="Solar power tower" /></a> The problem is that we mostly use this technology for the wrong purpose. In today's solar thermal plants, solar energy is converted into steam (via a steam boiler), which is then converted into electricity (via a steam turbine that drives an electric generator).</p>
<p>This process is just as inefficient as converting electricity into heat: two-thirds of energy gets lost when converted from steam to electricity. This is one of the main reasons why the use of solar thermal energy to produce electricity is only cost-effective in deserts.</p>
<p>----------------------------------------------------------------------------------------------------------------------------------------------</p>
<p style="text-align: right; padding-left: 120px;"><span style="font-size: 13pt;">If were to use concentrated solar power to generate heat instead of converting this heat into electricity - a process in which two thirds of energy gets lost - the technology would be cost-effective anywhere on Earth</span></p>
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<p>If we were to use solar thermal plants to generate heat instead of converting this heat into electricity, the technology could deliver energy 3 times cheaper than it does today and become cost-effective also in less sunny regions. The crucial difference between solar thermal electricity and other renewables producing electricity is that solar thermal actually starts with heat energy. Thus, contrary to other renewables, the cost of heat energy using the technology is far lower than the cost of electricity, and so it can compete with burning fossil fuels at the thermal level.</p>
<p><span style="font-size: 13pt;">Low temperature solar heat</span></p>
<p>This can be demonstrated by flat plate collectors and evacuated tube collectors, which are used for domestic hot water preparation and (to a lesser extent) interior space heating. This technology is used without any conversion losses and is cost-competitive with fossil fuels almost anywhere on Earth. According to the <a href="http://www.iea-shc.org/publications/downloads/Solar_Heat_Worldwide-2011.pdf" target="_blank">2011 update</a> of the International Energy Agency's <a href="http://www.iea-shc.org/" target="_blank">Solar Heating and Cooling Programme</a> (IEA-SHC), solar thermal heat is now the second most important renewable energy source following wind, and a much more important energy source than photovoltaics and solar thermal power plants. Almost 60 percent of solar thermal heat capacity can be found in China and another 20 percent is in Europe. The US and Canada (where the main application is to heat swimming pools) account for less than 9 percent.</p>
<p><a href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301538ff5af76970b-pi"><img style="display: block; margin-left: auto; margin-right: auto;" title="Renewable energies comparison capacity" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301538ff5af76970b-500wi" alt="Renewable energies comparison capacity" /></a></p>
<p>Sweden, Denmark, Spain, Germany and Austria have the most sophisticated markets for different solar thermal applications, including large-scale plants for district heating and a small but growing number of systems for air conditioning and cooling (using an <a href="http://en.wikipedia.org/wiki/Absorption_heat_pump" target="_blank">absorption chiller</a>). By the end of 2009, 115 solar supported district heating networks and 11 solar supported cooling systems were installed in Europe. Canada, Saudi Arabia and Singapore have also built a few large-scale solar heat systems for producing hot water, space heating and cooling.<strong>&nbsp;</strong></p>
<p><span style="font-size: 13pt;">The potential of solar heat for industrial processes</span><strong><br /></strong></p>
<p>Without a doubt, solar heat for domestic purposes should continue to be encouraged and a lot of potential remains. But it does not stop there. According to a 2008 report (pdf), which analyses the situation in Europe, the&nbsp;<a href="http://www.iea-shc.org/publications/downloads/task33-Potential_for_Solar_Heat_in_Industrial_Processes.pdf" target="_blank">potential for solar heat in industrial processes</a> is even larger than in the domestic market. About 30 percent of industrial heat demand in Europe is below 100 °C (212 °F), which could be delivered by commercially available flat plate collectors (&lt; 80 °C) and evacuated tube collectors (&lt; 120 °C) currently used for domestic purposes.</p>
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<p style="text-align: right; padding-left: 120px;"><span style="font-size: 13pt;">Almost 60 percent of heat demand in Euopean industry could be covered by already available and cost-effective technology using an inexhaustible renewable energy source that has no ecological disadvantages whatsoever.</span></p>
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<p>Another 27 percent of industrial heat demand requires medium temperatures (100 to 400 °C or 212 to 752 °F), which could be reached by improved versions of these collectors (up to 160 °C, see <a href="http://www.iea-ship.org/documents/Medium_Temperature_Collectors_Task33-IV__email.pdf" target="_blank">this document</a>) and by commercially available solar concentrator technologies now mostly used for electricity production: parabolic troughs, parabolic dishes and linear concentrating Fresnel collectors.</p>
<p><a href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301538fe94554970b-pi"><img style="display: block; margin-left: auto; margin-right: auto;" title="Industrial heat demand" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301538fe94554970b-500wi" alt="Industrial heat demand" /></a></p>
<p>This means that at least 57 percent of heat demand in European industry (or almost 40 percent of total industrial energy demand) could be covered by available and cost-effective technology using an inexhaustible renewable energy source that has no ecological disadvantages whatsoever. The capital costs (and embodied energy) of this would be much less than replacing a similar amount of fossil fuel energy use with solar panels or wind turbines. And of course, it could be done anywhere, not just in Europe.</p>
<p><strong>&nbsp;</strong><span style="font-size: 13pt;">Solar heat in industry: existing applications</span><strong><br /></strong></p>
<p><a style="float: left;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330153901a8a03970b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330153901a8a03970b" style="width: 250px; margin: 0px 5px 5px 0px;" title="Sopogy-micro-csp" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330153901a8a03970b-250wi" alt="Sopogy-micro-csp" /></a> At low and medium temperatures, solar heat can be used for industrial processes in several ways. It can provide warm water for processes like bottle washing or chemical processes. Secondly, it can provide hot air for drying and baking processes, for instance in the food and paper industries. Thirdly, it can generate steam that can be fed into steam heat distribution networks, which are widely used in many industries. The interesting thing is that in all these applications, the existing industrial machinery and distribution infrastructure remains in place. Only the energy source is replaced.</p>
<p>Some manufacturers have started marketing their solar concentrator technologies for the use of heat generation in industry, in addition to their application as electricity generators. Examples are <a href="http://sopogy.com/" target="_blank">Sopogy</a> (a Hawaian company that sells modular parabolic trough systems - picture above), the <a href="http://www.solar-power-group.de/" target="_blank">Solar Power Group</a> (a German company that sells linear concentrating Fresnel collectors) and&nbsp; <a href="http://www.hdsolar.com/" target="_blank">HelioDynamics</a> (an American seller offering similar technology - picture below).</p>
<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833014e8a0d965f970d-pi"><img class="asset asset-image at-xid-6a00e0099229e88833014e8a0d965f970d" style="margin: 0px 0px 5px 5px;" title="Heliodynamics solar power" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833014e8a0d965f970d-320wi" alt="Heliodynamics solar power" /></a> Installations for the use of solar industrial process heat are still rare, but they exist. German heating systems manufacturer Viessmann installed 260 m² of its own flat plate collectors on its factory in France to provide hot water for a chemical process, taking a first step towards producing renewable energy using renewable energy. A solar thermal plant based on 1,900 m² of parabolic troughs provides steam for a pharmaceutical plant in Egypt. A similar solar thermal plant was built for a dairy plant in Greece. A food processing facility in California has 5,000&nbsp;m² of parabolic troughs to produce steam used in the manufacturing process. Several industrial applications of solar heat have been built in India, using both flat plate collectors and concentrator technologies.</p>
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<p style="text-align: right; padding-left: 120px;"><span style="font-size: 13pt;">At low and medium temperatures, solar heat can be applied to industrial processes using already existing machinery and heat distribution pipelines</span></p>
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<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833015433d1b4ac970c-pi"><br /></a> <a style="float: left;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833015433d1b4ac970c-pi"><img class="asset asset-image at-xid-6a00e0099229e88833015433d1b4ac970c" style="margin: 0px 5px 5px 0px;" title="Arun solar concentrator" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833015433d1b4ac970c-320wi" alt="Arun solar concentrator" /></a> A solar concentrator system called <a href="http://www.clique.in/arun.html" target="_blank">ARUN</a> - a Fresnel parabolic reflector with point focus that delivers temperatures from 80 to 400 °C - has been installed in six industries, ranging from a dairy plant to an automobile manufacturer (picture on the left). India also has several large solar cooking facilities for community kitchens (schools, hospitals, factories, religious centres). The largest one consists of <a href="http://wka3.de/bildergalerie/bildergalerie1/cgi-bin/einzeln_pix.pl?solar=1&amp;bild=Unbenannt-34.jpg&amp;stop=stop" target="_blank">84 parabolic dish systems</a> reaching temperatures of up to 650 °C and producing up to 38,500 meals per day. The largest solar process heat application to date was recently installed in Hangzhou, China, where 13,000 m² of solar collectors on the roof of a textile factory provide hot water for a dyeing process. The <a href="http://www.solarthermalworld.org/" target="_blank">Global Solar Thermal Energy Council</a> is continually updating its list of <a href="http://www.solarthermalworld.org/taxonomy/term/528?module=browse" target="_blank">new industrial applications</a> of solar heat.</p>
<p><span style="font-size: 13pt;">Renewables building renewables</span><strong><br /></strong></p>
<p>The remaining 43 percent of industrial heat demand in Europe is above 400 °C (752 °F). These include many of the industrial processes that we need to manufacture renewable energy sources (wind turbines, solar panels, flat plate collectors and solar concentrators) as well as other green technologies (like LEDs, batteries and bicycles). Examples include the production of glass (requiring temperatures up to 1,575 °C) and cement (1,450 °C), the recycling of aluminum (660 °C) and steel (1,520 °C), the production of steel (1,800 °C) and aluminum (2,000 °C) from mined ores, the firing of ceramics (1,000 to 1,400 °C) and the manufacturing of silicon microchips and solar cells (1,900°C ).</p>
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<p style="text-align: right; padding-left: 120px;"><span style="font-size: 13pt;">Solar furnaces can reach temperatures up to 3,500 °C (6,332 </span>°<span style="font-size: 13pt;">F), enough to produce microchips, solar cells, carbon nanotubes, hydrogen and all metals</span></p>
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<p>These temperatures can be achieved by solar concentrator technology. Linear reflectors (parabolic trough systems and linear concentrating Fresnel collectors) are limited to temperatures of about 400 °C, but point concentrators can reach higher temperatures. These include parabolic dish systems, solar power towers, and solar furnaces - which are basically a combination of power towers and parabolic dish systems.&nbsp;</p>
<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833015433cec036970c-pi"><img style="margin: 0px 0px 5px 5px;" title="Solar furnace france" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833015433cec036970c-500wi" alt="Solar furnace france" /></a> Solar furnaces can produce temperatures up to 3,500 °C (6,332 °F), enough to manufacture microchips, solar cells, carbon nanotubes, hydrogen and all metals (including tungsten which has a melting point of 3,400 °C). These temperatures can be achieved in just a few seconds - see this <a href="http://www.youtube.com/watch?v=8tt7RG3UR4c&amp;feature=player_embedded" target="_blank">short video</a> of a solar furnace melting steel. The most powerful solar furnace is the one <a href="http://fr.wikipedia.org/wiki/Four_solaire_d%27Odeillo" target="_blank">at Odeillo in France</a>, built in 1970, which concentrates the light of the sun 10,000 times and has a power output of 1 MW.</p>
<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833015433d154dd970c-pi"><img style="margin: 0px 0px 5px 5px;" title="Solar furnace uzbeskistan" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833015433d154dd970c-500wi" alt="Solar furnace uzbeskistan" /></a>More than 60 heliostats (only one is seen on the picture above, in the lower righthand corner) direct the rays of the sun onto a parabolic mirror of more than 1,800 square metres, from which they are concentrated on a focal point with a diameter of only 40 centimetres in the tower in front of it. A <a href="http://www.flickr.com/photos/22988688@N00/221904120" target="_blank">similar solar furnace stands in Uzbekistan</a>, built in 1976, but it is slightly less powerful due to lower solar insolation in the region. The picture on the right shows it in action, melting metal.</p>
<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833014e89f939c3970d-pi"><img style="margin: 0px 0px 5px 5px;" title="Solar furnace PSI switzerland" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833014e89f939c3970d-500wi" alt="Solar furnace PSI switzerland" /></a>You don't need such an enormous structure to achieve high temperatures. Several smaller solar furnaces have been built, often using only one heliostat. They reach similar or only slightly lower temperatures (usually between 1,500 and 3,000 °C) than the giants pictured above, though at significantly lower power outputs (between 15 and 60 kW). They can perform most of the same processes as the large solar furnaces, but processing smaller amounts of materials or chemicals.</p>
<p>Examples of smaller solar furnaces can be found at the Paul Scherrer Institute in Switzerland (pictured above), the National Renewable Energies Laboratory in the USA, the Plataforma Solar de Almería in Spain, the German Aerospace Center in Germany, and the Weizmann Institute of Science in Israel (a solar power tower). They have concentration ratios between 4,000 and 10,000. In solar concentration, the temperature is proportional to the degree of concentration, whereas power will be proportional to size and efficiency (which is mostly determined by temperature).<strong>&nbsp;</strong></p>
<p><span style="font-size: 13pt;">Solar energy improves product quality</span></p>
<p>Solar furnaces not only have the potential to replace fossil fuels for the energy-intensive production of construction materials, chemicals, and high-tech products like <a href="http://www.lowtechmagazine.com/2009/06/embodied-energy-of-digital-technology.html" target="_blank">microchips</a> and <a href="http://www.lowtechmagazine.com/2008/03/the-ugly-side-o.html" target="_blank">solar cells</a>, but they also offer additional benefits because of their pure combustion and selective heating capacities. A 1999 research paper describes the <a href="http://www.sciencedirect.com/science/article/pii/0927024895000992" target="_blank">manufacturing of silicon solar cells using a solar furnace</a>, concluding that "solar furnace processing of silicon solar cells has the potential to improve cell efficiency, reduce cell fabrication costs, and also be an environmentally friendly manufacturing method. We have also demonstrated that a solar furnace can be used to achieve solid-phase crystallization of amorphous silicon at very high speed."</p>
<p>As opposed to low and medium temperature processes in industry, where only the energy source is replaced and the machinery and distribution infrastructure can remain in place, most high temperature solar heat applications require new machinery. Furnaces and kilns have to be rebuilt. Some efforts have been made. The Paul Sherrer Institute in Switzerland designed several <a href="http://infolib.hua.edu.vn/Fulltext/ChuyenDe/ChuyenDe07/CDe112/53.pdf" target="_blank">solar powered lime and cement kilns</a> (pdf), and research concluded that they could become <a href="http://www.pre.ethz.ch/publications/journals/full/j105.pdf" target="_blank">cost-competitive with a fossil fuel powered kiln</a> (pdf) following some further technological improvements. Again, the quality of the product turned out to be better using solar energy, eliminating combustion by-products.</p>
<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833015433d1b4ac970c-pi"><br /></a><span style="font-size: 13pt;">Low-tech, open source solar concentrators</span></p>
<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833014e8976095e970d-pi"><img style="margin: 0px 0px 5px 5px;" title="Solar fire 1" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833014e8976095e970d-500wi" alt="Solar fire 1" /></a>Though existing solar funaces prove that anything could be produced using direct solar heat instead of fossil fuels, this is not yet possible in a cost-effective way (it is cheaper to use fossil fuels). However, since solar furnaces could produce all materials needed to build more solar furnaces, they might become cost-effective even without technical improvements if fossil fuels become more expensive.</p>
<p>Moreover, the capital costs of solar concentrators are decreasing quickly following some recent innovations aimed at simplifying the technology. These might not only lead to cheaper high temperature solar heat concentrators in the future, but they also make the use of solar heat for medium temperatures more affordable and competitive today.</p>
<p>The most spectacular example is the <a href="http://www.solarfire.org/" target="_blank">Solar Fire P32</a> (picture above and pictures below), a solar concentrator developed in 2010 by the French NGO the Solar Fire Project. It is an open source design (joining forces with the <a href="http://www.notechmagazine.com/2011/05/how-to-build-your-own-industrial-civilization.html" target="_blank">Open Source Ecology project</a>), but the machine can also be bought for 7,500 <span style="text-decoration: line-through;">euro</span> dollar - less than the price of an <a href="http://www.lowtechmagazine.com/2009/04/small-windmills-test-results.html" target="_blank">urban wind turbine</a>.</p>
<p><a style="float: left;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301543355ff59970c-pi"><img style="width: 200px; margin: 0px 5px 5px 0px;" title="Solar fire 3" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301543355ff59970c-200wi" alt="Solar fire 3" /></a>The Solar Fire P32 is built using simple, abundant and non-toxic materials. Contrary to most other modern green technologies, there is no need for rare earth metals or advanced tools that are not found in an average metal workshop. Essentially, this is a renewable source of heat energy analogous to <a href="http://www.notechmagazine.com/windmills/" target="_blank">home made windmills</a> used to produce mechanical energy.</p>
<p><a style="float: left;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301543355ff59970c-pi"><br /></a>The machine can deliver up to 15 kW and can reach a focal temperature of 700 °C (1,292 °F), enough to melt (and thus recycle) aluminum, the material that is used to make its reflectors. This means that you could use a Solar Fire P32 to make another Solar Fire P32. Or almost. The receiver and the supporting structure are made of steel, which requires a higher melting temperature to recycle. However, the structure could as well be made of wood, <a href="http://www.lowtechmagazine.com/2012/02/basketry-the-art-of-producing-sustainable-consumer-goods.html" target="_self">basketry</a> or aluminum, and the steel receiver could easily be scavenged material. The use of glass improves the workings of the device, but is not strictly necessary.</p>
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<p style="text-align: right; padding-left: 270px;"><span style="font-size: 13pt;">The Solar Fire P32 costs 7,500 dollar and can be used to make another Solar Fire P32</span></p>
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<p>The Solar Fire P32 is composed of 360 small mirrors with a total surface of 32 square metres, focusing sunlight on a steam boiler above them. The steam can be used directly to purify large quantities of water, boil milk, produce edible oils, make charcoal, bake bricks, make paper, and so on.</p>
<p><span style="font-size: 13pt;">Increasing energy autonomy</span></p>
<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301538f82d599970b-pi"><img style="margin: 0px 0px 5px 5px;" title="Solar fire 6" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301538f82d599970b-500wi" alt="Solar fire 6" /></a>The steam can also drive a steam engine to directly power a water pump, oil and grain mills, cotton spinning, or any other stationary application requiring mechanical power. Connected to a steam generator, the machine can also generate electricity (up to 3 kW). These two last applications involve conversion losses, but they are interesting additions for those who want to achieve energy independence, especially in regions where there is lots of sun but no wind. The machine can produce heat, electricity and direct mechanical energy.<strong>&nbsp;</strong></p>
<p>The Solar Fire P32 is - in the first place - aimed at developing countries and designed to be cost-effective compared to burning coal and wood, reducing deforestation and pollution, increasing energy autonomy, and providing an energy source at the scale of traditional practices and small industries. It has been built in Mexico, Cuba, Burkina-Faso, Mali, India and Kenya, but also in Texas, France and Canada. Obviously, the design could also be useful in the developed world, where the supply of fossil fuels might not remain as easily accessible as it is today.&nbsp;</p>
<p><span style="font-size: 13pt;">Simplifying technology</span></p>
<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833014e89761c55970d-pi"><img style="width: 200px; margin: 0px 0px 5px 5px;" title="Solar fire 5" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833014e89761c55970d-200wi" alt="Solar fire 5" /></a>Apart from the additional equipment that is required to generate electricity, conventional solar concentrator technologies demand heavy capital investments for several reasons. Parabolic trough systems and parabolic dish systems require curved mirrors that are expensive to produce. Moreover, these mirrors cannot be manufactured locally and often have to be transported over long distances, increasing costs further. In both systems the curved mirrors are large and heavy, requiring rigid frames, strong foundations, powerful hydraulics and sophisticated tracking systems to follow the sun. In parabolic dish systems, the heat engine or steam boiler is part of the moving structure, increasing weight and thus making things even worse.</p>
<p>Solar power towers - which were invented in 1878 - solve some of these issues: they use nearly flat mirrors and all mirrors share one stationary receiver. But, they require the construction of a large tower building. Last but not least, all of these systems have very high land requirements because of overshadowing issues. Linear Fresnel concentrators use (mostly) flat mirrors, have simpler tracking systems and are more compact, but they can only reach temperatures of 250 °C (using relatively low-tech materials) or 450 °C (using sophisticated technology).</p>
<p><a style="float: left;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330153901adb67970b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330153901adb67970b" style="width: 250px; margin: 0px 5px 5px 0px;" title="Sundrop jewelry melting glass" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330153901adb67970b-250wi" alt="Sundrop jewelry melting glass" /></a>The Solar Fire is a Fresnel parabolic reflector with point focus, just like ARUN - but unlike that machine it is placed horizontally and the receiver does not have to be turned together with the mirrors, resulting in light weight and high wind resistance. The machine uses slightly curved mirrors, achieved by mechanical bending which can be done on the spot. Sun tracking of the mirrors is done by hand, eliminating the need for electronics and electric motors altogether (multiple mirrors can be turned at once using hand operated wheels). This might sound crude, but for industrial applications the machine has to be supervised anyway.</p>
<p>And because it is open source, it can be further improved by anyone. Eerik Wissenz, the designer of the machine, thinks this is the only way: "Companies pursuing patents for solar collectors have fallen into a complexity trap. Since solar energy is free it is far simpler to add 5 percent more surface area instead of creating complex machines too expensive to be commercially viable. Solar fire concentration is so simple it cannot be patented."</p>
<p><span style="font-size: 13pt;">Low-tech solar furnaces</span></p>
<p>High temperature solar furnaces can be low-tech autonomous systems, too. One example is the large magnifying glass used by <a href="http://www.sundropjewelry.com/" target="_blank">Sundrop Jewelry</a>, which reaches high enough temperatures to melt coloured bottle glass into handcrafted jewelry. Of course the power output is low, making this installation useless if you want to produce industrial quantities of glass. But it shows that solar heat can be used on any scale.</p>
<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833014e8a0e2ac2970d-pi"><img style="margin: 0px 0px 5px 5px;" title="Solar_sinter_01" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833014e8a0e2ac2970d-320wi" alt="Solar_sinter_01" /></a>Another example is the <a href="http://www.markuskayser.com/" target="_blank">Solar Sinter Project</a> by Markus Kayser, in which glass is produced using only sunlight and desert sand. I would like to quote the artist here: "Whilst not providing definitive answers, this experiment aims to provide a point of departure for fresh thinking".</p>
<p><span style="font-size: 13pt;">Storage</span></p>
<p>How can you power factories using an energy source that is not always available? Solar insolation varies throughout the day and the seasons, and there is no sun at night. Moreover, solar concentrator technologies only work with unscattered sunlight, which means that a passing cloud stops energy production. This raises two questions. Some industrial processes work fine with intermittent energy supply, but how do you guarantee an uninterrupted supply of energy to a process that requires it? And what do you do when there is no sun at all for a week?</p>
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<p style="text-align: right; padding-left: 240px;"><span style="font-size: 13pt;">Storing heat is much cheaper and more efficient than storing electricity in a battery</span></p>
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<p>There are three ways to deal with the intermittency of solar power. The first solution is to design hybrid systems: make solar and already existing energy sources work together. This is how most of today's solar thermal power plants work. In this scenario, which offers a solution for both short and long term storage, industrial processes are powered by solar heat whenever it is available. When it is not, solar energy is instantly replaced by fossil fuels or electricity. It is not an ideal solution, but it could save large amounts of energy. And we don't need new technology to make it work.</p>
<p><a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301539013f2f5970b-pi"><img class="asset asset-image at-xid-6a00e0099229e8883301539013f2f5970b" style="margin: 0px 0px 5px 5px;" title="Sopogy thermal storage" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301539013f2f5970b-320wi" alt="Sopogy thermal storage" /></a> The second strategy is to store solar energy so that it can be used to smooth out industrial processes (analogous to a flywheel for smoothing out mechanical processes) and to guarantee energy supply on cloudy days or at night. Storage of heat is much cheaper and more efficient than storage of electricity. The most low-tech way is to store heat in well-insulated water reservoirs - another technology that is more than 100 years old. The disadvantages are that you need quite a lot of space, and that water storage only works up to a temperature of 100 °C (212 °F). There are more compact ways to store heat at higher temperatures, for example by using <a href="http://www.saint-gobain-solar-power.com/solar-thermal-storage-norpro-9" target="_blank">ceramics</a> or phase-changing materials (certain salts). These storage media are already used in one solar thermal power plant, but they would be even more efficient if used in a thermal only system. Innovative technology could further improve heat storage.</p>
<p><span style="font-size: 13pt;">Storing work instead of energy</span></p>
<p>The third way to deal with the intermittency of solar heat is to store <em>work</em> instead of <em>energy</em>. We let our factories work when the sun shines, and only when the sun shines. Just like we wait for a sunny day to do the laundry, we could wait for a sunny day to bake bricks, recycle metal or produce smartphones. Industrial production would be concentrated in summer months. Of course, there is a price to pay. Industrial production would be lower. But considering the fact that our energy and environmental problems are largely caused by overproduction and overconsumption of goods, this is not as far-fetched as it might seem.</p>
<p>Combining all three strategies could be a solution. In that scenario we would run part of our factories only when the sun shines (and <a href="http://www.lowtechmagazine.com/2009/10/history-of-industrial-windmills.html" target="_blank">when the wind blows</a>), using heat storage, fossil fuels, biomass or electricity to smooth out industrial processes if necessary. Critical goods could be produced continuously combining solar heat and heat storage, fossil fuels, or biomass. Of course, not all climates are blessed with enough sun to make solar heat a viable option to power the whole industry. But since many people are now talking about outsourcing electricity production to desert regions, we could just as well move our factories to regions where there is plenty of sun. It is much more efficient to transport manufactured goods over large distances than to transport electricity.</p>
<p><strong> <a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301538ffefdcb970b-pi"><br /></a> </strong></p>
<p><span style="font-size: 13pt;">Solar powered enhanced oil recovery</span></p>
<p>As always, a sustainable technology can be used for unsustainable purposes. Solar heat is a great way to get more oil out of fields that are now considered exhausted. Getting that remaining oil out using gas would cost more money and energy than the oil could return, but using a free source of energy changes everything.</p>
<p><strong> <a style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301538ffefdcb970b-pi"><img class="asset asset-image at-xid-6a00e0099229e8883301538ffefdcb970b" style="margin: 0px 0px 5px 5px;" title="GlassPoint" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301538ffefdcb970b-500wi" alt="GlassPoint" /></a> </strong></p>
<p>At least one company specializes in this application. <a href="http://www.glasspoint.com/" target="_blank">Glasspoint</a>, a US firm originally founded to use solar heat for <a href="http://www.google.com/url?sa=t&amp;source=web&amp;cd=1&amp;ved=0CBQQFjAA&amp;url=http%3A%2F%2Fwww.theoildrum.com%2Fnode%2F6264&amp;rct=j&amp;q=drying%20gypsum%20wall%20board%20oil%20drum&amp;ei=FKAoTu7OMMSLswap0vC9CQ&amp;usg=AFQjCNEcCfnSdKDbMrT3wYVPvb5KPLdNfQ&amp;cad=rja" target="_blank">drying gypsum wall board</a>, has seen remarkable growth promoting "Solar Enhanced Oil Recovery".</p>
<p>This has been tried before, but they use an innovative technology: parabolic trough mirrors suspended from the ceiling of enormous glasshouse structures that are equipped with robotic cleaning systems. Because they are protected from wind, sand and dust by the greenhouse, the mirrors can be made extremely light and without protective glass layers - lowering their costs and increasing their efficiency. The steam that is generated by the solar heat is pumped into the oil reservoir. The more sun there is, the more oil will come to the surface. Only 20 to 40 percent of an oil field can be recovered using standard techniques, but as much as 60 to 80 percent can be recovered using solar heat. In the end, solar heat could thus increase fossil fuel production and CO2-emissions.</p>
<p>Kris De Decker (edited by Rachel Meyer)</p>
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<p><span style="font-size: 13pt;">Sources, inspiration &amp; more information:</span></p>
<ul>
<li><a href="http://www.solarfire.org/The-Thermal-Problem" target="_blank">The thermal problem and the solar (thermal) solution</a>, Eerik Wissenz, 2011.</li>
<li><a href="http://www.builditsolar.com/Projects/Concentrating/concentrating.htm" target="_blank">Concentrating Solar Concentrators</a> at the Build it Solar Site. Lots of links to DIY-projects. Thanks to Paul Nash.</li>
<li><a href="http://www.eolss.net/ebooks/Sample%20Chapters/C08/E6-106-06-00.pdf" target="_blank">High temperature solar collectors</a>, Robert Pitz-Paal, in 'Solar Energy Conversion and Photoenergy Systems'.</li>
<li><a href="http://www.amazon.com/gp/product/4871877124/ref=as_li_qf_sp_asin_tl?ie=UTF8&amp;tag=lowtemagaz-20&amp;linkCode=as2&amp;camp=217145&amp;creative=399373&amp;creativeASIN=4871877124">Direct Use of the Sun's Energy</a><img class="uuhwewivwknfowzjrmyi" style="border: none !important; margin: 0px !important;" src="http://www.assoc-amazon.com/e/ir?t=lowtemagaz-20&amp;l=as2&amp;o=1&amp;a=4871877124&amp;camp=217145&amp;creative=399373" alt="" width="1" height="1" border="0" />, Farrington Daniels, 1964.&nbsp;</li>
<li><a href="http://www.iea-shc.org/task33/" target="_blank">Task 33 - Solar heat for industrial processes</a>, Solar Heating and Cooling Programme, International Energy Agency.</li>
<li><a href="http://www.iea-shc.org/publications/downloads/task33-Potential_for_Solar_Heat_in_Industrial_Processes.pdf" target="_blank">Potential for Solar Heat in Industrial Processes</a> (pdf), Claudia Vannoni, Riccardo Battisti and Serena Drigo, Task 33</li>
<li><a href="http://www.iea-shc.org/publications/downloads/task33-Process_Heat_Collectors.pdf" target="_blank">Process Heat Collectors - state of the art within task 33/IV</a> (pdf), Werner Weiss and Matthias Rommel</li>
<li><a href="http://www.pre.ethz.ch/publications/0_pdf/books/Solar_Thermochemical_Process_Technology.pdf" target="_blank">Solar thermochemical process technology</a>, Aldo Steinfeld &amp; Robert Palumbo, 2001</li>
<li><a href="http://www.iea-shc.org/publications/downloads/Solar_Heat_Worldwide-2011.pdf" target="_blank">Solar Heat Worldwide 2011</a> (pdf), SHC, Werner Weiss &amp; franz Mauthner, may 2011</li>
<li><a href="http://www.solarthermalworld.org/node/2966" target="_blank">The Value of Concentrating Solar Power and Thermal Energy Storage</a>, National Renewable Laboratory, 2010</li>
<li><a href="http://www.cd3wd.com/cd3wd_40/vita/solrconc/en/solrconc.htm" target="_blank">Understanding solar collectors</a>, George Kaplan, 1985</li>
<li><a href="http://www.solarthermalworld.org/" target="_blank">Global Solar Thermal Energy Council</a>.</li>
<li><a href="http://www.solar-process-heat.eu" target="_blank">So-Pro</a>: European project on solar process heat</li>
<li><a href="http://www.estif.org/home/" target="_blank">European Solar Thermal Industry Association</a></li>
<li><a href="http://www.sollab.eu" target="_blank">The European Alliance SolLab</a></li>
<li><a href="http://www.solarpaces.org/inicio.php" target="_blank">SolarPACES</a></li>
<li><a href="http://www.solarpaces.org/CSP_Technology/csp_technology.htm" target="_blank">CSP- how it works</a></li>
</ul>
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<p><span style="font-size: 13pt;"><a href="http://www.lowtechmagazine.com/2015/12/fruit-walls-urban-farming.html"> <img class="asset asset-image at-xid-6a00e0099229e8883301b8d18853b7970c img-responsive" title="Montreuil peaches" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301b8d18853b7970c-320wi" alt="Montreuil peaches" /></a><br /></span></p>
<p><span style="font-size: 13pt;">Related articles:</span></p>
<ul>
<li><a href="http://www.lowtechmagazine.com/2015/12/fruit-walls-urban-farming.html">Fruit walls: urban solar farming in the 1600s</a></li>
<li><a href="http://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html">Reinventing the greenhouse</a></li>
<li><a href="http://www.lowtechmagazine.com/2012/03/solar-oriented-cities-1-the-solar-envelope.html" target="_self">The solar envelope</a>: how to heat and cool cities without fossil fuels</li>
<li><a href="http://www.lowtechmagazine.com/2015/04/how-sustainable-is-pv-solar-power.html" target="_self">How sustainable is PV solar power?</a></li>
<li><a href="http://www.lowtechmagazine.com/2011/09/peat-and-coal-fossil-fuels-in-pre-industrial-times.html" target="_self">Medieval smokestacks</a>: thermal energy in pre-industrial times</li>
<li><a href="http://www.lowtechmagazine.com/2009/10/history-of-industrial-windmills.html" target="_self">Wind powered factories</a>: the history (and future) of industrial windmills.</li>
<li><a href="http://www.lowtechmagazine.com/2011/05/pedal-powered-farms-and-factories.html" target="_self">Pedal powered farms and factories:</a> the forgotten future of the stationary bicycle machine</li>
</ul>
<p><a href="http://www.lowtechmagazine.com/" target="_self">Main page</a>.</p>
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Bike powered electricity generators are not sustainabletag:typepad.com,2003:post-6a00e0099229e8883301538ea99dd6970b2011-05-25T14:32:24+02:002019-03-02T13:20:15+01:00Pedaling a modern stationary bicycle to produce electricity might be a great work-out, but in many cases, it is not sustainable. While humans are rather inefficient engines converting food into work, this is not the problem we want to address here; people have to move in order to stay healthy, so we might as well use that energy to operate machinery. The trouble is that the present approach to pedal power results in highly inefficient machines. There are two ways to power a device by pedalling. You can power it directly through a mechanical connection - as was the case with all pedal powered machines for sale at the turn of the 20th century. Or, you can pedal to generate...kris de decker
<div xmlns="http://www.w3.org/1999/xhtml"><p><a class="asset-img-link" style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03a2d99200d-pi"><img class="asset asset-image at-xid-6a00e0099229e888330224e03a2d99200d img-responsive" style="width: 150px; margin: 0px 0px 5px 5px;" alt="Windstream power generator" title="Windstream power generator" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03a2d99200d-150wi" /></a> Pedaling a modern stationary bicycle to produce electricity might be a great work-out, but in many cases, it is not sustainable.</p>
<p>While humans are rather inefficient engines converting food into work, this is not the problem we want to address here; people have to move in order to stay healthy, so we might as well use that energy to operate machinery.</p>
<p>The trouble is that the present approach to pedal power results in highly inefficient machines. </p>
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<p>&nbsp;</p>
<p>There are two ways to power a device by pedalling. You can power it directly through a mechanical connection - as was the case with <a href="http://www.lowtechmagazine.com/2011/05/history-of-pedal-powered-machines.html" target="_self">all pedal powered machines for sale at the turn of the 20th century</a>. Or, you can pedal to generate electricity, which is then used to power the device. <a href="http://www.lowtechmagazine.com/2011/05/pedal-powered-farms-and-factories.html" target="_self">In the 1970s, most research was aimed at direct mechanical power transmission</a>. Today, the interest in pedal powered machines is almost exclusively aimed at generating electricity, for instance for charging cell phones and laptops - products that did not even exist in the 1970s.</p>
<p>With one exception (the '<a href="http://bikeblender.com/products/" target="_blank" rel="noopener noreferrer">Fender Blender</a>', a pedalled powered machine to make smoothies), the only pedal powered machinery that is now commercially available in the western world (offered by <a href="http://www.windstreampower.com/" target="_blank" rel="noopener noreferrer">Windstream</a>, <a href="http://www.econvergence.net/" target="_blank" rel="noopener noreferrer">Convergence Tech</a> and <a href="http://www.magnificentrevolution.org/shop/" target="_blank" rel="noopener noreferrer">Magnificent Revolution</a>) are stands to fit your bike to, connected to an electric motor/generator and a battery - a combination that can quickly convert your regular road bicycle into an electricity generator. These are also the pedal powered machines which are used for educational and arts projects, like <a href="http://rockthebike.com/pedal-powered-stage-gear" target="_blank" rel="noopener noreferrer">powering</a> a <a href="http://www.futurespark.com.au/about-future-spark" target="_blank" rel="noopener noreferrer">music concert</a>, a <a href="http://electricpedals.com/events/pedal-powered-cinema-2/" target="_blank" rel="noopener noreferrer">cinema</a> <a href="https://prod.buzzbnk.org/ProjectDetails.aspx?projectId=5" target="_blank" rel="noopener noreferrer">projection</a> or a <a href="http://www.computerworld.com.au/article/201723/mit_students_power_supercomputer_bicycles/" target="_blank" rel="noopener noreferrer">supercomputer</a>, or <a href="http://electricpedals.com/2011/04/02/dundonald-primary-school-pedal-powered-workshop/" target="_blank" rel="noopener noreferrer">teaching kids</a> the difference in energy use between, for instance, an incandescent light bulb and an energy saving lamp.</p>
<p><a class="asset-img-link" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03a2da6200d-pi"><img class="asset asset-image at-xid-6a00e0099229e888330224e03a2da6200d img-responsive" alt="Pedal power generator" title="Pedal power generator" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03a2da6200d-320wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p>In an effort to raise awareness about energy use and global warming, the BBC even made a TV-programme in which <a href="http://www.youtube.com/watch?v=C93cL_zDVIM" target="_blank" rel="noopener noreferrer">an entire household was powered via these generators</a>, with 80 cyclists generating up to 14 kW. These multi-person pedal power generators were <a href="http://www.appropedia.org/CCAT_pedal_powered_energy_generator" target="_blank" rel="noopener noreferrer">pioneered in the 1970s</a> by the Campus Center for Appropriate Technology (CCAT).</p>
<h2 style="text-align: center;"><span style="font-size: 12pt; color: #c00000;"><strong>Generating electricity is very inefficient</strong></span></h2>
<p>There are several problems with the present-day approach to pedal power. First of all, it is important to know that generating electricity is far from the most efficient way to apply pedal power, due to the internal energy losses in the battery, the battery management system, other electronic parts, and the motor/generator.</p>
<p>These energy losses add up quickly: 10 to 35 percent in the battery, 10 to 20 percent in the motor/generator and 5 to 15 percent in the converter (which converts direct current to alternate current). (Sources: <a href="http://www.soe.uoguelph.ca/webfiles/gej/articles/GEJ_001-008-016_Gilmore_Human_Power.pdf" target="_blank" rel="noopener noreferrer">1</a>/<a href="http://photovoltaics.sandia.gov/docs/PDF/batpapsteve.pdf" target="_blank" rel="noopener noreferrer">2</a>/<a href="http://www.itacanet.org/eng/elec/battery/battery.pdf" target="_blank" rel="noopener noreferrer">3</a>). The energy loss in the voltage regulator (or DC to DC converter, which prevents you from blowing up the battery) is about 25 percent (sources: <a href="http://www.magnificentrevolution.org/shop/parts-accessories/" target="_blank" rel="noopener noreferrer">1</a>/<a href="http://www.batteryspace.com/dc-dcregulatormodule13-17vdcto12vdc4ampratewithremovableheatsink.aspx" target="_blank" rel="noopener noreferrer">2</a>).</p>
<p>This means that the total energy loss in a pedal powered generator will be 42 to 67.5 percent (calculation example for highest loss: 100 watt input = 80 watt after 20% loss in motor/generator = 57.5 watts after 25% energy loss in voltage regulator = 37.5 watts after 35% loss in battery = 32.5 watts after 15% loss in converter = 32.5 watts output = efficiency of 32.5% or energy loss of 67.5%).</p>
<blockquote>
<p style="text-align: right;"><span style="font-size: 13pt;">You have to pedal 2 to 3 times as hard or as long if you choose to power a device via electricity compared to powering the same device mechanically</span></p>
</blockquote>
<p>Furthermore, there will be an additional slight loss as the battery stands idle, and the charge efficiency (also known as "charge acceptance" or "coulombic efficiency") of the battery will deteriorate over time. And to make the calculation complete, you should actually also include the energy loss in the electrical device that you are powering (we won't do that here).</p>
<p>An energy loss of 42 to 67.5 percent of naturally means that it takes 42 to 67.5 percent more effort or time to power a device (say, a blender) via electricity compared to powering the same device mechanically. This can be considered an acceptable loss if you are using solar panels or a wind turbine connected to a battery as an energy source, but it becomes rather problematic when you have to deliver the energy yourself.</p>
<p>If you produce 100 watts of power and 42 to 67.5 percent is lost in the conversion, there is only 32.5 to 58 watts left to power the device. If you power the same device mechanically, you deliver 100 watts straight to it. You thus have to pedal 2 to 3 times as hard or as long if you choose to take the intermediate step of generating electricity and storing it in a battery.</p>
<h2 style="text-align: center;"><span style="font-size: 12pt; color: #c00000;"><strong>Traditional bicycles were not made to generate stationary power</strong></span></h2>
<p>It does not stop here. The second problem with the present approach to pedal power is that it uses a traditional bicycle on a training stand instead of a pedal powered machine built from scratch - as was the case at the end of the 19th century. Of course, using a traditional bicycle has its advantages, but again it should be realized that this approach is considerably less efficient.</p>
<p><a class="asset-img-link" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330223c84b8851200c-pi"><img class="asset asset-image at-xid-6a00e0099229e888330223c84b8851200c img-responsive" alt="AmpGenerator" title="AmpGenerator" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330223c84b8851200c-320wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p>One reason is the use of a so-called friction drive - the rear bicycle wheel acts upon the small roller of the motor/generator. While chain and belt drives (used in late 19th century pedal powered machines) have an efficiency of up to 98 percent, a friction drive is only 80 to 90 percent efficient (and wears much faster). This energy loss should be added to the 42 to 67.5 percent efficiency loss calculated above, which rises to 48 to 73.5 percent. Low tyre pressure will further decrease efficiency.</p>
<p>It should be noted that there is also energy loss in the bicycle itself: your pedals are not attached to the rear wheel itself. You turn a sprocket, which turns a chain, which turns a sprocket, which turns the rear wheel. So, on top of the efficiency loss of the friction drive should be added the efficiency loss of a chain drive (plus the energy loss in the derailleur, if your bike has one).</p>
<blockquote>
<p style="text-align: right; padding-left: 120px;"><span style="font-size: 13pt;">Additional energy losses occur when using a racing bike or a mountain bike</span></p>
</blockquote>
<p><span style="font-size: 13pt;"><span style="font-size: 11pt;">Connecting a bike chain directly to the generator would prevent the energy loss of the friction drive, but it implies that you have to adapt the bicycle - destroying the whole concept of today's commercially available pedal generators.</span></span></p>
<h2 style="text-align: center;"><span style="font-size: 12pt; color: #c00000;"><strong>Racing bicycles</strong></span></h2>
<p>Additional energy losses can occur when using a road bicycle to generate electricity. For example, the picture accompanying the Windstream generator shows a racing bicycle. This is a very bad choice, because the position of a rider on a racing bike is aimed to reduce wind resistance. Tests on ergometers (stationary bikes used to measure the power output of cyclists) have shown that pedalling in such a position is only about 80 percent as effective compared to a normal upright position, again resulting in considerable energy loss.</p>
<p><img class="asset asset-image at-xid-6a00e0099229e888330223c84b887d200c img-responsive" alt="Windstream bike power generator" title="Windstream bike power generator" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330223c84b887d200c-320wi" style="display: block; margin-left: auto; margin-right: auto;" /></p>
<p>On the road the rider position on a racing bicycle is beneficial because of the large importance of air resistance. However, on a stationary pedalling machine this position has no advantage whatsoever. The popular mountain bike is equally disadvantageous because of the corrugated tyres, which of course lower the efficiency of the friction drive. In short, while using a road bicycle to generate electricity has the advantage that you can use your own bike, this does not mean you can use just <em>any</em> bike.</p>
<h2 style="text-align: center;"><span style="color: #c00000; font-size: 12pt;"><strong>Flywheel</strong></span></h2>
<p>Another important drawback of using a common road bicycle is the absence of a flywheel - a heavy disc made of concrete, wood or steel that continues to generate power after it has been put in motion.</p>
<p>In a pedal powered machine built from scratch, like the ones used at the turn of the 20th century, the flywheel applies the function of the rear bicycle wheel in the training stand (although the flywheel is mostly placed at the front of the machine). The pedaller powers the flywheel, and the flywheel powers the machine (which can be a mechanical device or a motor/generator to produce electricity).&nbsp;</p>
<p><img class="asset asset-image at-xid-6a00e0099229e888330224e03a2e12200d img-responsive" alt="Concrete flywheel" title="Concrete flywheel" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224e03a2e12200d-320wi" style="display: block; margin-left: auto; margin-right: auto;" /></p>
<p>Why is a flywheel advantageous? Because there is an important difference between riding a bicycle on the road and pedalling a stationary machine. If we are pedalling, the power exerted by our feet on the pedals is inconsistent. It peaks every 180 degrees of crank rotation, and because the two cranks are placed 180 degrees out of phase this results in two power peaks per turn of the crank.</p>
<p>Similarly, there are dead spots in between at the top and bottom position of the pedals (to be correct this minimum torque is not zero but about one third of the maximum).</p>
<blockquote>
<p style="text-align: right; padding-left: 60px;"><span style="font-size: 13pt;">On a stationary bicycle without a flywheel, the natural pedalling rhythm results in jerky motion, limiting the energy output of the rider</span></p>
</blockquote>
<p>On a bicycle, this uneven exertion has little effect because of the inertia of both bike and rider. But on a stationary pedal powered machine, this natural pedalling rhythm results in jerky motion and additional stress on parts.</p>
<p>Because of its large mass and rotational speed, the flywheel evens out the difference between power peaks and dead spots. Evening out the power input means that the rider tires less quickly and can thus generate more power. The obvious disadvantage of a flywheel is that it is heavy - from 10 to 80 kg for stationary pedal powered machines - and thus not exactly mobile.</p>
<h2 style="text-align: center;"><span style="font-size: 12pt; color: #c00000;"><strong>Generating electricity is not eco-friendly</strong></span></h2>
<p>Generating electricity is not only ineffiicient, it also makes pedal power less sustainable, less robust and more costly. To begin with, batteries have to be manufactured, and they have to be replaced regularly. This requires energy, which can completely negate the ecological advantage of pedal power.</p>
<p><img class="asset asset-image at-xid-6a00e0099229e888330224df333d56200b img-responsive" alt="Chassis and flywheel mayapedal" title="Chassis and flywheel mayapedal" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224df333d56200b-320wi" style="display: block; margin-left: auto; margin-right: auto;" /></p>
<p>According to <a href="http://newenergyindia.org/Energy%20Payback%20time_Opinion%20Page.pdf" target="_blank" rel="noopener noreferrer">this research paper</a> (pdf), the embodied energy of a 150Wh lead-acid battery (like the one offered with the Windstream pedal power generator) is at least 37,500 Wh, which equals 250 full charges of the battery (more sources: <a href="http://light.lbl.gov/pubs/tr/lumina-tr9-embodied-energy.pdf" target="_blank" rel="noopener noreferrer">1</a>/<a href="http://www.sciencedirect.com/science?_ob=ArticleURL&amp;_udi=B6V2S-4WGJKHB-4&amp;_user=10&amp;_coverDate=09%2F30%2F2009&amp;_rdoc=1&amp;_fmt=high&amp;_orig=gateway&amp;_origin=gateway&amp;_sort=d&amp;_docanchor=&amp;view=c&amp;_searchStrId=1754671808&amp;_rerunOrigin=google&amp;_acct=C000050221&amp;_version=1&amp;_urlVersion=0&amp;_userid=10&amp;md5=9ca92696d87e4122d51b62d219552f10&amp;searchtype=a" target="_blank" rel="noopener noreferrer">2</a>). In other words: if you can deliver 75 watts of power to the battery, you have to pedal for 500 hours in order to generate the energy that was needed to manufacture the battery.</p>
<p>Because the life expectancy of a lead-acid battery can be as low as 300 discharge/charge cycles (sources: <a href="http://batteryuniversity.com/learn/article/can_the_lead_acid_battery_compete_in_modern_times" target="_blank" rel="noopener noreferrer">1</a>/<a href="http://www.itacanet.org/eng/elec/battery/battery.pdf" target="_blank" rel="noopener noreferrer">2</a>), you are basically pedalling to produce the energy required to manufacture the battery. If you also factor in <a href="http://www.lowtechmagazine.com/2009/06/embodied-energy-of-digital-technology.html" target="_self">the embodied energy of other electronics and parts</a>, the ecological advantage of a pedal powered generator connected to a battery becomes rather doubtful. It might costs more energy than it delivers.</p>
<blockquote>
<p style="text-align: right; padding-left: 180px;"><span style="font-size: 13pt;">A pedal powered generator might cost more energy than it delivers</span></p>
</blockquote>
<p><span style="font-size: 13pt;"><span style="font-size: 11pt;">Of course, it also takes energy to manufacture a pedal powered machine that does not take the intermediate step of generating electricity. This concern lies mainly with the production of steel, and quite a lot of it. The commercially available Fender Blender mentioned earlier weighs 25kg (55 pounds).</span></span></p>
<p>If made from recycled steel, and using <a href="http://www.lowtechmagazine.com/what-is-the-embodied-energy-of-materials.html" target="_blank" rel="noopener noreferrer">these figures</a> to calculate the embodied energy of steel, this comes down to an energy cost of at least 41,625 Wh, slightly more than the battery needed for the electricity generator.</p>
<p>If freshly made steel is used, the embodied energy is at least 138,750 Wh (3.7 times the embodied energy of a single battery). However, these machines can last at least 100 years (pedal powered machines surviving from the late 19th century are still in use), while the battery of the electricity generator has to be replaced every few years.</p>
<p><a class="asset-img-link" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330224df333d7a200b-pi"><img class="asset asset-image at-xid-6a00e0099229e888330224df333d7a200b img-responsive" alt="Lead acid battery" title="Lead acid battery" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224df333d7a200b-320wi" style="display: block; margin-left: auto; margin-right: auto;" /></a></p>
<p>If we ignore the embodied energy of other parts than the battery (both training stand and electronics), and take a life expectancy of 4 years for the battery (rather optimistic), a pedalled powered generator would require an embodied energy of 937,500 Wh over the course of 100 years - 6.7 to 22.5 more than a mechanical unit.</p>
<p>Moreover, it is easy to make the frame for a mechanical pedal powered machine from scavenged materials, bringing the embodied energy down to almost zero, while this is an impossibility for the batteries. Never mind that in addition, the toxicity of the materials is another thing to consider.&nbsp;</p>
<h2 style="text-align: center;"><span style="font-size: 12pt; color: #c00000;"><strong>Generating electricity is less robust and more expensive</strong></span></h2>
<p>While a pedal powered machine is the most robust and resilient energy source around if you power devices mechanically, this advantage is lost when you start generating electricity. Few people can manufacture batteries themselves, so you remain dependent on a regular supply of replacement batteries.</p>
<p>Furthermore, the electronic parts of the machine (voltage regulator, motor/generator, converter) can break down and are not easy to make or repair yourself either - contrary to old-fashioned pedal powered machines, which can be fixed yourself with readily available materials. Mechanical pedal powered machines are generally even easier to repair and maintain than bicycles.</p>
<p><img class="asset asset-image at-xid-6a00e0099229e888330224df333d94200b img-responsive" alt="Barnes velocipede amazon" title="Barnes velocipede amazon" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330224df333d94200b-320wi" style="display: block; margin-left: auto; margin-right: auto;" /></p>
<p>The extra components also make pedal generators more expensive. The commercially available models sell for $700 to more than $1000, not including the necessary replacements of the battery over time. Even if you make your own pedal power generator, the costs add up. The 2008 book '<a href="http://www.amazon.com/gp/product/0865716013/ref=as_li_qf_sp_asin_tl?ie=UTF8&amp;tag=lowtemagaz-20&amp;linkCode=as2&amp;camp=217145&amp;creative=399349&amp;creativeASIN=0865716013">The Human-Powered Home: Choosing Muscles Over Motors</a>', which has plans for several kinds of pedal powered machines, estimates the costs of a DIY generator at about $50 (using scavenged parts) to $350 (using new parts), not including a bicycle stand and replacement batteries. Another <a href="http://www.motherearthnews.com/Renewable-Energy/2008-10-01/Pedal-Powered-Generators.aspx?page=4" target="_blank" rel="noopener noreferrer">source</a> estimates the cost at $600.</p>
<p>The mechanical pedal powered machines in the book can be built for $10 to $50 (the washing machine being more expensive at $100), everything included. While the only commercially available mechanical pedal powered machine today is very expensive too (the Fender Blender sells for $1,700), the high cost is almost entirely due to the steel frame - which, as mentioned, could easily be replaced by the frame of an old exercise bike, or built oneself from scavenged materials. Moreover, there are no additional costs for replacement batteries and the machine is built to last for a very long time.</p>
<p><span style="font-size: 12pt;"><strong>Continue reading: <a href="http://www.lowtechmagazine.com/2011/05/pedal-powered-farms-and-factories.html" target="_self">How to make pedal power efficient and sustainable?</a></strong></span></p>
<p><strong> <a style="float: left;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833014e888c79ea970d-pi"><img class="asset asset-image at-xid-6a00e0099229e88833014e888c79ea970d" style="margin: 0px 5px 5px 0px;" title="Christoph thetard flywheel of kitchen device" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833014e888c79ea970d-320wi" alt="Christoph thetard flywheel of kitchen device" /></a> </strong>One way to solve the large energy losses of pedal power generators is not to produce electricity at all and power devices mechanically, whenever possible. Another way - the only way for devices that cannot be powered via a direct mechanical connection because they do not rely on rotary motion - is to make the generation of electricity more efficient.</p>
<p>This can be done by building a pedal powered generator from scratch instead of using a road bicycle, and/or by ditching one or several electronic components in the power transmission chain. All approaches can be combined, resulting in a pedal power unit that can power a multitude of mechanical devices and generate electricity comparatively efficiently. <a href="http://www.lowtechmagazine.com/2011/05/pedal-powered-farms-and-factories.html" target="_self">Read more</a>.</p>
<p>Kris De Decker (edited by Shameez Joubert)</p>
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<p><span style="font-size: 14pt;"><a href="http://www.lowtechmagazine.com/2018/05/ditch-the-batteries-off-the-grid-compressed-air-energy-storage.html">DITCH THE BATTERIES: OFF-GRID COMPRESSED AIR ENERGY STORAGE</a></span></p>
<p><a class="asset-img-link" style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e888330223c84b87bf200c-pi"><img class="asset asset-image at-xid-6a00e0099229e888330223c84b87bf200c img-responsive" style="width: 200px; margin: 0px 0px 5px 5px;" alt="Diy compressed air" title="Diy compressed air" src="https://krisdedecker.typepad.com/.a/6a00e0099229e888330223c84b87bf200c-200wi" /></a>Going off-grid? Think twice before you invest in a battery system. Compressed air energy storage is the sustainable and resilient alternative to batteries, with much longer life expectancy, lower life cycle costs, technical simplicity, and low maintenance.</p>
<p>Designing a compressed air energy storage system that combines high efficiency with small storage size is not self-explanatory, but a growing number of researchers show that it can be done.</p>
<p><img title="Streep" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833017d405b927d970c-800wi" alt="Streep" border="0" /></p>
<p><span style="font-size: 14pt;"><a href="http://www.humanpowerplant.be/2017/09/prototype-hydro-pneumatic-human-power-plant.html">PROTOTYPE OF A HYDRO-PNEUMATIC HUMAN POWER PLANT</a></span></p>
<p><a class="asset-img-link" style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301b8d2ac9efa970c-pi"><img class="asset asset-image at-xid-6a00e0099229e8883301b8d2ac9efa970c img-responsive" style="width: 200px; margin: 0px 0px 5px 5px;" alt="6a00e0099229e8883301b8d2aad892970c-250wi" title="6a00e0099229e8883301b8d2aad892970c-250wi" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301b8d2ac9efa970c-200wi" /></a>The Human Power Plant is a working prototype of a muscular power generator, manned by a group of people. It is an all-round off-the-grid solution, which can supply energy in the form of electricity, water under pressure, and compressed air. It is built from simple and durable parts.</p>
<p>These days, we have automated and motorised even the smallest physical efforts. At the same time, we go to the gym to keep in shape, generating energy that’s wasted. The Human Power Plant restores the connection between physical exercise and energy use.</p>
<p><a href="http://krisdedecker.typepad.com/.a/6a00e0099229e88833017d405b927d970c-pi"><img title="Streep" src="https://krisdedecker.typepad.com/.a/6a00e0099229e88833017d405b927d970c-800wi" alt="Streep" border="0" /></a></p>
<p><span style="font-size: 14pt;"><a href="http://www.lowtechmagazine.com/2017/05/could-we-run-modern-society-on-human-power-alone.html">COULD WE RUN MODERN SOCIETY ON HUMAN POWER ALONE</a>? </span></p>
<p><span style="font-size: 11pt;"> <a class="asset-img-link" style="float: right;" href="http://krisdedecker.typepad.com/.a/6a00e0099229e8883301b8d287467d970c-pi"><img class="asset asset-image at-xid-6a00e0099229e8883301b8d287467d970c img-responsive" style="width: 200px; margin: 0px 0px 5px 5px;" title="Shower and laundry floor human powered student building" src="https://krisdedecker.typepad.com/.a/6a00e0099229e8883301b8d287467d970c-200wi" alt="Shower and laundry floor human powered student building" /></a>The <a href="http://www.humanpowerplant.be" rel="noopener noreferrer" target="_blank">Human Power Plant</a> project investigates the possibilities of human energy production in a modern society. It plans to convert a 22-floor building on the campus of Utrecht University into an entirely human powered student community. </span></p>
<p><span style="font-size: 11pt;">With a combination of low-tech solutions, lifestyle changes, and some exercise, it demonstrates that 750 students can live a fossil fuel free life on campus.</span></p>
<p>--------------------------------------------------------------------------------------------------------------</p>
<p><strong><span style="font-size: 12pt;">Sources (in order of importance)</span></strong></p>
<ul>
<li>"<a href="http://www.amazon.com/gp/product/0878571787/ref=as_li_tf_tl?ie=UTF8&amp;tag=lowtemagaz-20&amp;linkCode=as2&amp;camp=217145&amp;creative=399349&amp;creativeASIN=0878571787">Pedal Power in Work, Leisure and Transportation</a>", edited by James McCullagh, Rodale Press, 1977. Still the best resource on pedal powered machines.</li>
<li>"<a href="http://www.amazon.com/gp/product/0865716013/ref=as_li_qf_sp_asin_tl?ie=UTF8&amp;tag=lowtemagaz-20&amp;linkCode=as2&amp;camp=217145&amp;creative=399349&amp;creativeASIN=0865716013">The Human-Powered Home: Choosing Muscles Over Motors</a><img class="uuhwewivwknfowzjrmyi" style="border: none !important; margin: 0px !important;" src="http://www.assoc-amazon.com/e/ir?t=lowtemagaz-20&amp;l=as2&amp;o=1&amp;a=0865716013&amp;camp=217145&amp;creative=399349" alt="" width="1" height="1" border="0" />", Tamara Dean, New Society Publishers, 2008. Very good book on human powered machines, both hand and foot powered. Includes half a dozen plans to convert bicycles into stationary pedal powered machines.</li>
<li>"<a href="http://www.amazon.com/gp/product/0262731541/ref=as_li_qf_sp_asin_tl?ie=UTF8&amp;tag=lowtemagaz-20&amp;linkCode=as2&amp;camp=217145&amp;creative=399349&amp;creativeASIN=0262731541">Bicycling Science</a><img class="uuhwewivwknfowzjrmyi" style="border: none !important; margin: 0px !important;" src="http://www.assoc-amazon.com/e/ir?t=lowtemagaz-20&amp;l=as2&amp;o=1&amp;a=0262731541&amp;camp=217145&amp;creative=399349" alt="" width="1" height="1" border="0" />", Third Edition, David Gordon Wilson, 2004</li>
<li>"<a href="http://pdf.usaid.gov/pdf_docs/PNAAN161.pdf" target="_blank" rel="noopener noreferrer">The Dynapod: a pedal power unit</a>" (pdf), Alex Weir, 1980. More <a href="http://www24.brinkster.com/alexweir/thresher/default.htm" target="_blank" rel="noopener noreferrer">here</a>.</li>
<li>"<a href="http://www.cd3wd.com/cd3wd_40/JF/JF_VE/SMALL/19-436.pdf" target="_blank" rel="noopener noreferrer">The use of pedal power for agriculture and transport in developing countries</a>" (pdf), David Weightman, Lanchester Polytechnic, 1976</li>
<li>"<a href="http://etd.ohiolink.edu/send-pdf.cgi/Cyders%20Timothy%20J.pdf?acc_num=ohiou1227199047" target="_blank" rel="noopener noreferrer">Design of a human-powered utility vehicle for developing communities</a>", Timothy J. Cyders, 2008</li>
<li>"<a href="http://books.google.com/books?id=TnwrAAAAYAAJ&amp;printsec=frontcover&amp;dq=Supplement,+energy+for+rural+development:+renewable+resources+and&amp;hl=nl&amp;ei=DnOrTeePBoTEsgaErZWcCA&amp;sa=X&amp;oi=book_result&amp;ct=result&amp;resnum=1&amp;ved=0CDEQ6AEwAA#v=onepage&amp;q&amp;f=false" target="_blank" rel="noopener noreferrer">Supplement, Energy for rural development</a>", National Research Council, 1981</li>
<li>"<a href="http://www.amazon.com/gp/product/1931626162/ref=as_li_qf_sp_asin_tl?ie=UTF8&amp;tag=lowtemagaz-20&amp;linkCode=as2&amp;camp=217145&amp;creative=399349&amp;creativeASIN=1931626162">Tales from the Blue Ox</a><img class="uuhwewivwknfowzjrmyi" style="border: none !important; margin: 0px !important;" src="http://www.assoc-amazon.com/e/ir?t=lowtemagaz-20&amp;l=as2&amp;o=1&amp;a=1931626162&amp;camp=217145&amp;creative=399349" alt="" width="1" height="1" border="0" /> ", Dan Brett, 2003</li>
<li>"<a href="http://www.notechmagazine.com/2010/10/bicycles-tricycles-an-elementary-treatise-on-their-design-and-construction-1896.html" target="_blank" rel="noopener noreferrer">Bicycles and tricycles</a>", Archibald Sharp, 1896</li>
<li>"<a href="http://www.ihpva.org/HParchive/PDF/31-v9n3-1991.pdf" target="_blank" rel="noopener noreferrer">In search of the massless flywheel</a>" (pdf), John S. Allen, Human Power (Fall/Winter 1991-1992)</li>
<li>"<a href="http://www.ihpva.org/HParchive/PDF/45-v13n2-1998.pdf" target="_blank" rel="noopener noreferrer">Design and development of a human-powered machine for the manufacture of lime-flyash-sand bricks</a>", J.P.Modak &amp; S.D.Moghe, Human Power (Spring 1998)</li>
<li>"<a href="http://130.15.85.212/proceedings/proceedings_WorldCongress/WorldCongress07/articles/sessions/papers/A983.pdf" target="_blank" rel="noopener noreferrer">Human Powered Flywheel Motor: concept, design, dynamics and applications</a>", J.P.Modak, 2007</li>
<li>"<a href="http://www.notechmagazine.com/2010/10/exhibiting-the-latest-progress-in-machines-motors-and-the-transmission-of-power-1892.html" target="_self">Modern mechanism: exhibiting the latest progress in machines, motors, and the transmission of power</a>", Benjamin Park, 1892</li>
<li>"<a href="http://www.motherearthnews.com/Renewable-Energy/2008-10-01/Pedal-Powered-Generators.aspx" target="_blank" rel="noopener noreferrer">Make electricity while you exercise</a>", Mother Earth News, 2008</li>
<li>"<a href="http://toolemera.com/catpdf/luther1920CAT.pdf" target="_blank" rel="noopener noreferrer">Luther's tool grinders</a>" (pdf, 5.8 MB), hand and foot powered grinders catalog. Hosted at <a href="http://toolemera.com/" target="_blank" rel="noopener noreferrer">Toolemera Blog</a>.</li>
<li>"<a href="http://toolemera.com/catpdf/melhuish1925CAT.pdf" target="_blank" rel="noopener noreferrer">Woodworkers' tools and machines</a>" (pdf, 29 MB), product catalogue no.25, 1884, Richard Melhuish Ltd., Tool and Machine Merchants, London. Hosted at <a href="http://toolemera.com/" target="_blank" rel="noopener noreferrer">Toolemera Blog</a>.</li>
<li>"<a href="http://books.google.com/books?id=X7X4A5efIooC&amp;pg=PA215&amp;lpg=PA215&amp;dq=needham+treadle&amp;source=bl&amp;ots=15p6kkUaRV&amp;sig=c9EUz06fVMihNBqpNEzv9xd4ZSE&amp;hl=en&amp;ei=wsDaTaPiAcyw8QORv6mEBQ&amp;sa=X&amp;oi=book_result&amp;ct=result&amp;resnum=1&amp;ved=0CBoQ6AEwAA#v=onepage&amp;q&amp;f=false" target="_blank" rel="noopener noreferrer">Science &amp; civilisation in China, Vol.5, Part 9</a>", Joseph Needham, 1988</li>
</ul>
<p><span style="font-size: 12pt;"><strong>Related articles:</strong></span></p>
<ul>
<li><a href="https://www.lowtechmagazine.com/2019/02/heat-your-house-with-a-water-brake-windmill.html">Heat your house with a water brake windmill</a></li>
<li><a href="http://www.lowtechmagazine.com/2016/04/slow-electricity-the-return-of-low-voltage-dc-power.html">Slow electricity: the return of DC power</a>?</li>
<li><a href="http://www.lowtechmagazine.com/2013/08/direct-hydropower.html" target="_self">Back to Basics: Direct Hydropower</a></li>
<li><a href="http://www.lowtechmagazine.com/2010/12/hand-powered-drilling-tools-and-machines.html" target="_self">Hand powered drilling tools and machines</a></li>
<li><a href="http://www.lowtechmagazine.com/2010/03/history-of-human-powered-cranes.html" target="_blank" rel="noopener noreferrer">Human powered cranes and lifting devices</a>: the sky is the limit</li>
<li>Short posts on <a href="http://www.notechmagazine.com/pedal-power/" target="_self">pedal power</a> can be found at <a href="http://www.notechmagazine.com/" target="_blank" rel="noopener noreferrer">No Tech Magazine</a></li>
<li><a href="http://www.notechmagazine.com/2011/11/when-low-tech-goes-ikea.html" target="_self">Full plans for a pedal powered juice extractor</a></li>
</ul>
<hr />
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<p>Low-tech Magazine makes the jump from web to paper. The first result is a&nbsp;<a href="http://www.lulu.com/shop/kris-de-decker/low-tech-magazine-20122018/paperback/product-24028679.html">710-page perfect-bound paperback</a>&nbsp;which is printed on demand and contains 37 of the most recent articles from the website (2012 to 2018). A second volume, collecting articles published between 2007 and 2011, will appear later this year.</p>
<p><span style="font-size: 18pt;"><strong><a href="https://www.lowtechmagazine.com/2019/03/printed-website.html">Read more: Low-tech Magazine: The Printed Website</a></strong>.&nbsp;</span></p>
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